I have a e-VGA 7900GS video card installed in a motherboard that only has a PCI-e x4 lane (not x16). How much will this hurt my performance? Like, is it 1/4 as fast or what?

Computer:
e-VGA 7900GS 256MB VC
pentium d805 2.66GHz
ASRock 880 dual pro mobo
corsair tiwn x 2 x 1gb
maxtor pata 60gb hdd

for a 7900GS....im guessing a performance loss of less that 5% (in games)

Here is a scaling test done on this site a few months back: http://www.tomshardware.co.uk/pci- [...] -2125.html

Im guessing its just the 8800 cards (and now the HD2900 cards) that make a fairly big difference in terms of 4x and 16x.

I have a 8600GTS, and I recetly replaced my Asrock 775 Dual-VSTA with a MSI P35 Platinum. I tried a few games and 3dmark05/06. PCI-E x4 was 10-15% slower. Of course, the more powerful your card is, the more it will be likely to be bottlenecked, but a 7900GS should be fine.

I also noticed that a few video issues disappeared since I switched to a x16 PCI-E port : corrupted polygons in some games, and sometimes random crashes during video playback/edition. seems the 8600gts doesn't like to run on PCI-E x4

i wouldn't trust that toms review one bit as it offered no analysis whatsoever nor any reliable data.(extremely limited tests)

however, my knowledge is far too limited to give a correct answer.

However, you do only have a sub 3ghz p4 and so you may be CPu limted(note NOT, I REPEAT NOT BOTTLENECKED) before yiu are GPU limited even with the limited interface.

The fact that there is not a definitive answer by toms or AFAIK any site on this question is shocking, absolutely shocking but there it is.

basically your guess is as good as mine.

Shouldn't give any NOTICEABLE decline in performance.