I know that the PCI-E 2.0 interface is backwards compatible with the PCI-E 1.0 interface. However, I'm wondering what high-end cards (e.g., GTX 400 series or better) will be backward compatible; do any of them require the extra bandwidth of PCI-E 2.0?
If PCI-E 2.0 support is optional, can I expect a GTX 460 1GB to outperform 2 x 8800 GTX 768MB in SLI on PCI-E 1.0? I would lose 512MB in VRAM but gain ~200MHz on the core clock, and more than double the 1800MHz effective memory clock to 3800MHz (not to mention DX11 support).
I feel that I would see a noticeable performance improvement. Is there any way to be sure without buying and benchmarking?