Is my CPU, bus, or Chipset Holding my 4870 back

I'm just wondering if anyone has any input on what might be holding back my 4870 1Gb card. My specs are as below. I was curious if these things need a fast CPU to push them. Or is it because I have a PCI-E 1.1 bus not 2.0. My understanding the bandwidth of the 1.1 bus still isn't even maximized and the difference might be slight if at all between 1.1 and 2.0. Or is it my 975x chipset causing some sort of bottleneck. Any input would be great. I have searched through the Futuremark ORB reports to see if I can see patterns but it's difficult to tell. I previously had an 8800GTS/512 (@750/1000) and the difference between the two is noticable but not what I expected. the FPS aren't much different at the same settings but I can seem to crank up AA and such on the 4870 more.

E6400@3.0ghz w/ Thermalright Ultra-120
Asus P5W DH Deluxe
4x1GB Crucial Ballistix PC6400 4-4-4-12
CoolMax 600W PSU
ASUS 4870 1GB Dark Knight(825/1050)
Dell 22" E228WFP
Seagate 250GB ES.2 & 250GB 7200.10
Creative X-Fi XtremeGamer