PCI-e 2.0 question and more

Hello, this is my first time posting on the forums! I kind of questions that concern more than video cards, so please move this to where ever it needs to go.

I was wondering if PCI-e 2.0 made any difference in gaming when compared to PCI-e x16. I just upgraded to a HD 4870 1gb card and am still getting <20 fps in the Sims 3 when zoomed in to the city. Logic tells me the game is cpu intensive and my E4400 with 2mb of L2 cache just isn't cutting it...but I wanted to make sure running that card in PCI-e x16 wasn't contributing to the problem.

I plan on upgrading to 4gb of ram (2x 2gb DRR-800), and the 64-bit version of Vista is on its way (according to Microsoft at least), but I'm stuck on my cpu / mobo situation. Should I upgrade the DS3R to a PCI-e 2.0 compliant one, or is x16 sufficient for now? Is it hampering my card?

Would keeping the board, getting 4gb of ram and an C2D E8400 solve my gaming problem?

My computer specs -

Intel C2D E4400
Gigabyte GA-P35-DS3R
Corsair XMS2 2GB (2 X 1 GB) DDR2 800
Sapphire HD 4870 1GB
Fortron Source 500 watt psu
WD SATA 3.0 gb/s 320 GB HD
Lite-on DVD-DL burner
Thermaltake SopranoRS black case
Windows Vista Home Premium - 32-bit

Thanks for any and all help so far.