AMD Radeon RX 6800 XT in mGPU: 2 x Big Navi GPUs = Insane Performance

Introduction & Radeon RX 6800 XT in mGPU

Anyone that knows me knows that I'm a huge multi-GPU and resolution/FPS nerd, so the second that I could try out Big Navi in multi-GPU mode I knew I had to. I did some preliminary testing with the Radeon RX 5700 XT in mGPU mode, but now it's time for Big Navi and the Radeon RX 6800 XT in mGPU mode -- and man, are you going to love these results.

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The answer to that is yes, very much so -- yes.

I thought I would do these tests a little differently -- so I switched out the Ryzen 7 3800X out of my ASUS Crosshair VIII HERO Wi-Fi motherboard -- and in with AMD's new Zen 3-powered Ryzen 9 5900X processor. Yes, the new Ryzen 9 5900X processor is powering these multi-GPU tests with Big Navi and the two Radeon RX 6800 XT cards in mGPU mode.

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AMD sent over their new Ryzen 9 5900X for these very types of articles, where you can see the GPUs totally unleashed -- we have a brand new kick ass Zen 3-powered processor, and 2 x Radeon RX 6800 XT graphics cards. This is about as Team Red as it gets.

I'm half way through the 8K benchmarking, so I'll have a follow up article on 8K that will by the looks of it, be just as impressive if not even more so, than the exciting numbers below.

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The two cards in question -- XFX's latest Radeon RX 6800 XT Speedster MERC 319, alongside AMD's own reference Radeon RX 6800 XT graphics card. Ain't it beautiful?!

CrossFire is Dead... Kinda... Mostly...

AMD kinda retired CrossFire and its branding -- but that doesn't mean mGPU is dead. mGPU is the new CrossFire, with 'mGPU' standing for multi-GPU, or multiple GPUs. When it works, like in the games I tested, the results are actually very mind blowing.

DX12 mGPU games are few and far between, so I tested a couple of games that I already owned, and purchased a few for the purposes of this testing. Let's kick it off!

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Cards Tested

The very second I received my second Radeon RX 6800 XT -- which is the XFX Radeon RX 6800 XT Speedster MERC 319 graphics card, I knew I had to test it in mGPU mode.

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In this round of testing I have got a bunch of different cards from both sides of the GPU fence, this includes:

• AMD Radeon RX 6800 XT in mGPU
• AMD Radeon RX 5700 XT in mGPU
• AMD Radeon RX 6800 XT
• AMD Radeon RX 5700 XT
• NVIDIA GeForce RTX 3090
• NVIDIA GeForce RTX 3080
• NVIDIA TITAN RTX
• NVIDIA GeForce RTX 2080 Ti

I started off with just a few cards, but thought I'd add in a few more -- I'll get this article out and then I've got a few more hours of testing and playing to get some SLI results in here. I'll post a follow-up article that covers SLI on the RTX 2080 Ti and GTX 1080 Ti in the next 1-2 days.

What We Benchmarked

I did a bit of searching for a list of games I could benchmark with games that actually support it, outside of CrossFire as the Radeon RX 6800 XT cards do not support that. I found this post on /r/AMD on Reddit, and tested a bunch of the games that were on that list.

This includes:

• Sniper Elite 4
• Strange Brigade
• Rise of the Tomb Raider
• Deus Ex: Mankind Divided

I've tested them at 1080p, 1440p, and 4K -- with some 8K results coming very soon.

Test System Specs

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Latest upgrade:

Sabrent sent over their huge Rocket Q 8TB NVMe PCIe M.2 2280 SSD, which will be my new Games install SSD inside of my main test bed.

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I've got a new upgrade inside of my GPU test bed before my change to a next-gen test bed, where I will be preparing for NVIDIA's next-gen Ampere graphics cards and AMD's next-gen RDNA 2 graphics cards.

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Sabrent helped out with some new storage for my GPU test beds, sending over a slew of crazy-fast Rocket NVMe PCIe M.2 2280 SSDs. I've got this installed into my GPU test bed as the new Games Storage drive, since games are so damn big now. Thanks to Sabrent, I've got 2TB of super-fast M.2 PCIe 3.0 x4 SSD storage now.

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Anthony's GPU Test System Specifications

I've recently upgraded my GPU test bed -- at least for now, until AMD's new Ryzen 9 5950X processor is unleashed then the final update for 2020 will happen and we'll be all good for RDNA 2 and future Ampere GPU releases. You can read my article here: TweakTown GPU Test Bed Upgrade for 2021, But Then Zen 3 Was Announced.

• CPU: AMD Ryzen 7 3800X (buy from Amazon)
• Motherboard: ASUS ROG X570 Crosshair VIII HERO (buy from Amazon)
• Cooler: CoolerMaster MasterLiquid ML360R RGB (buy from Amazon)
• RAM: G.SKILL Trident Z NEO RGB 32GB (4x8GB) (F4-3600C18Q-32GTZN) (buy from Amazon)
• SSD: Sabrent 2TB Rocket NVMe PCIe 4.0 M.2 2280 (buy from Amazon)
• PSU: be quiet! Dark Power Pro 11 1200W (buy from Amazon)
• Case: InWin X-Frame 2.0
• OS: Microsoft Windows 10 Professional x64 (buy from Amazon)

Benchmarks - 1080p

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Benchmarks - 1440p

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Benchmarks - 4K

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Final Thoughts

Alright, how damn good are those results -- amazing stuff.

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I'm only doing this because I have review samples here to play around with and make this type of content, and I do not endorse multi-GPU setups these days. Single graphics cards are far better when you have to combat multi-GPU issues like micro stuttering, a massive lack of support with games, and a million other things -- power supplies, heat, noise.

But from a purely technological and nerd point of view -- so right up my alley, really -- we have a no-other-way-to-describe-it but a f***ing insane first start with Sniper Elite 4 at 1080p -- a monster 586FPS. This is 200FPS more than the GeForce RTX 3090, and just under twice as much as the single RX 6800 XT.

I also tested dual Radeon RX 5700 XTs which came out at just under 300FPS, while a single RX 5700 XT scores 151FPS. What we're seeing here is near-perfect scaling with the AMD Radeon graphics cards, beyond impressive to say the least. Strange Brigade is another big fan of that mGPU lovin' with 433FPS average from the RX 6800 XT in mGPU, beating the RTX 3090 by 90FPS.

Sniper Elite 4 continues to impress at 1440p with a huge 448FPS, double the 232FPS of a single RX 6800 XT -- and over double the RX 5700 XT in mGPU which is crazy. The GeForce RTX 3090 on the other hand has 284FPS average, while the RTX 3080 has 260FPS.

Strange Brigade has AMD shining in 1440p as well with 404FPS from the RX 6800 XT in mGPU, this is a huge result as the RTX 3090 only achieves 257FPS in comparison. Hell, even two Radeon RX 5700 XTs in mGPU mode only reach 220FPS -- up from the single card at 114FPS.

255FPS in 4K with Sniper Elite 4 felt really impressive to play, so buttery smooth -- while the RTX 3090 has 171FPS and the single RX 6800 XT with 119FPS. Strange Bridge continues to kill it at 4K with 278FPS average, up from the 158FPS on the RTX 3090 and 144FPS on the RX 6800 XT.

Rise of the Tomb Raider and Deus Ex: Mankind Divided have great scaling at 4K too, with Rise of the Tomb Raider hitting 204FPS average at 4K compared to just 113FPS with a single RX 6800 XT -- while Deus Ex: Mankind Divided hits 111FPS on RX 6800 XT in mGPU while the single RX 6800 XT reaches 70FPS.

Wrapping Up

I would never recommend dual-GPU cards for most people, but for those who love to have the very best -- playing around with a new Ryzen 9 5900X + Radeon RX 6800 XT in mGPU is a load of fun. Seeing the type of scaling in all resolutions in some of some (very) select games is very impressive.

It's not for everyone, but coming at it from a technological point of view -- AMD has impressive things to show here with mGPU on Big Navi. I wish it was used more, and were in more games going forward. It would be nice to sell it to enthusiasts, and to people who upgrade.

AMD could let you use an older card as help for your new card, offloading certain tasks along the way -- I think a good path forward with this is ray tracing. Offloading the ray tracing to another card, freeing up your main graphics card for pure graphics grunt.

But still, I'd love to see proper full mGPU support so that if you truly wanted to push 4K 120FPS in every single game... you could. I had virtually no stuttering at all in my testing, which was very impressive to see -- I wish I could run RX 6800 XT in mGPU in everything, because it would replace my RTX 3090.

Sigh... this is so exciting on one hand (these results) and so incredibly sad on the other (mGPU gaming is virtually dead).