Gfx on PCIe x16 (at x4)

Hi,
I have a Mercury PI945GZD mobo...with a PCIe x16 (runnning at x4 speed) slot. I wanted to add a graphics card to my system for arnd 2.5k. Now, since its running at x4, I wanted to know if it will have any adverse effects on such a low budget graphics card ?

Also plz suggest some good graphics cards in the range both from both Nvidia & ATI...