The CPU limitation issue is a very real one and can't be ignored. It's ignorant to think that even more budget friendly setups like the HD 6850 in Crossfire aren't going to be impacted by a CPU limitation, as at this price AMD really give us a huge amount of performance.
There's a few ways to combat a CPU limitation, though, and it's not by just increasing your CPU speed. The idea is that you want to put more load on the video cards and this can be done really in three ways. Up the in-game detail up higher than what it was at previously is one. If that's not an option, start to look at turning on AA and AF which really place a lot more pressure on your cards.
The final way is to increase the resolution you're gaming at, again, by placing more pressure on the video cards. You can clearly see with intensive games like Aliens vs. Predator the performance at 1920 x 1200 on our CPU at 3.06GHz is the same as it is at 4.2GHz while we're running more voltage through the CPU and possibly shortening the life. So what reason is there to overclock the CPU that high in this kind of a situation? There isn't one really.
When you really begin to break it down, though, the times we hit a CPU limitation we're already getting fantastic performance in games. Resident Evil 5 is a prime example. At 1680 x 1050 and our CPU at 3.06GHz we've got an average FPS of 178, while at 4.2GHz we've got an average FPS off 223.
Sure, that's a great gain, but that extra performance isn't going to make the game any better for you. Even in a situation where you're using a 120Hz monitor, you're at a number that's well and truly comfortable when at 3.06GHz.
I don't want to give the impression that buying a faster CPU is a waste of money, as we know that there's more to the purchase of a CPU than just gaming. But it's important to know that under situations where your video detail is high, the added speed of not just a few hundred MHz, but more than a GHz at time, can yield almost no performance increase when it comes to your actual FPS. Of course, as you climb up to higher end video card setups that come in at an excess of $1,000, then the more speed is going to be appreciated. That's something we may look at when the HD 6900 series begin to arrive.