Welcome to the forum.
Are you looking for a video card that offers better pc gaming performance?
How much are you willing to spend (in US dollars) for a new video card?
Are you looking for a single, higher end video card with more performance than a GTX 560 SLI setup?
Do you have a preference for Nvidia cards? Radeon cards?
Check out PCI Express 2.0 vs 3.0 GPU Gaming Performance Review
There have been a lot of threads in the ASRock forum where the motherboard had problems recognizing a gen 3.0 video card in the gen 3.0 pcie slot but didn't have problems running the same card in a gen 2.0 pcie slot. As I recall, Sapphire video cards seemed to have the most problems. Sometimes a replacement video card solved the problem, sometimes ASRock tech support needed to provide a newer beta bios to solve the problem.
Your best real world performance will be with memory speeds in the 1600 - 1866MHz range.
Higher memory speeds are good for benchmarking bragging rights but little else.
See Does DDR3 Memory Speed Really Matter with Ivy Bridge or Sandy Bridge? for more information.
Samsung 30nm memory has been excellent and trouble free with many systems. It is low voltage 1600MHz memory that often overclocks up to 2400MHz with standard 1.60 voltage settings. I don't know if 16GB of the Samsung memory will easily overclock this high.
There might be a few very intensive applications (encoding, photo manipulation, Digital Audio Workstation, etc.) that might have a bit more real world performance with 2000MHz or higher memory speeds. How fast are you willing to spend?