We used PerformanceTest 6.1 by PassMark which you can find out more information about here. It has a handy Advanced Networking section which is perfect for our testing.
Doing our best to emulate a real-world performance scenario, I setup a "server" running Windows 7 Ultimate (x64) Server, (Eurocom Panther Server Xeon W5590, 12GB DDR3, 3x 500GB HDDs RAID5) and the client PCs were an MSI Wind 200 With built-in Intel 802.11n (Intel WiFi Link 5100 AGN) adapter and a HTPC computer (MSI H55 motherboard, Intel Core i5 661, 4GB DDR3 1333 memory and a Patriot SSD).
Additionally we threw in a Seagate BlackArmor NAS 440 as a video storage server for MVK files.
Testing of something like a Powerline adapter is pretty simple. You plug both in and run a bandwidth testing benchmark like Passmark as well as pushing some real world data over it. We also tested this against an 802.11n wireless network using the same tools, just to see if we saw a performance difference.
You will notice that the Powerline kits are able to maintain a very consistent speed over their connection, while the wireless can quickly degrade over distance and based on other interference factors. We saw much more consistent performance over the Powerline network for streaming video and audio (including 1080p streaming).