the memory used by video card is actually a different type from the usual memory sticks mentioned on mobo's specs. For instance, currenty I'm running an LGA 775 motherboard with Core 2 Duo E 6750. This mobo only support DDR2.
With that setting, I also have a GTS 450 running just fine. The things that usually bottleneck is usually your CPU or the PCIE speed, for example running a PCIE 2.0 VGA card on a PCIE 1.0 motherboard.
And of course you'll get Phsyx and DX11. It has nothing to do with specs. I played Arkham Asylum and Arkham City with above specs with Physx just fine. Of course sometimes the framerate will drop (depends on the situation of your game, like having Batman surrounded by 30 thugs) when you enable Physx.
Oh, and yeah, of course you can run AMD graphic cards on Intel platforms, just like running NVidia cards on AMD platforms.