9800 gx2 on dell xps 650i motherboard

Hey guys, I am in the market for a prebuilt desktop from a major brand and the xps 630 caught my eye. I don't need the greatest and latest but I figured the gx2 would suffice. My question is with the butchered x16 lanes to x8 does it cripple the gx2s performance? If anyone could recommend some other good value prebuilts that would be great I think I feel comfortable enough to upgrade ram and the graphics card myself but that's it.