The PCIe slot is only 4x though (with a 16x connector), and this does have an effect on graphics performance in some situations. Also, some people have reported issues when using PCIe graphics cards - it seems only certain cards will work with it. I wouldn't go for it myself due to these problems, but if you really need what your asking for this is probably your only option.
I second it, system as per sig. No problems. Also used a 6600GT AGP and it was fine. Board is not an Overclocker. Am getting 5500 in '06 on a GTO which on benchmarks at least is not showing much of a bottleneck with the PCI-Ex4