PCI express 3.0 is a new BUS that will only work if you have an compatible motherboard and you are using an IVY bridge processor, so if you are thinking in using it, that is required, but there is no performance difference in GPUS from pci 3.0 8x or 16x from the pci 2.0 16x... at least not for now.
What would you suggest because i 3D game but i have a HD3D ready smartmonitor but have a gtx570 that i was using with my DLP for N3Dvision but now have gotten a new tv that nivida doesn't support 3D vision on so now i need a AMD GPU because im using my HD3D ready smart monitor again.
first of all, i think that you can use the 570 to see 3D there, the same way AMD does, download third party driver like IZ3D, and others... it may not work with nvidia 3D Vision but it will certainly work with third party drivers.
but all you need to do is change the GPU if you really want an AMD gpu, you can easily use a new 3.0 GPU on your 2.0 Motherboard without any BUS performance bottlenecks. since the 3.0 and 2.0 are the same for now.