Does under-powering a vid card have large effect on performance?

Hey guys,

I have an ATI HD 2900 1gb vid card. im running it off my 600w PSU, with 2x6-pin pci-e connectors going into it. its recommended you need 1x8-pin and 1x6-pin. 600w it still fine to have it working, but is underpowering it that much going to make a large impact on performance. in other words, if i go get me the larger PSU i have my eyes on, 850w, will my performance in games increase?

Cheers

I think those other pins are just for overclockingRandom__Guy

Correct - the 8 pin is needed to unlock the overclocking features on the 2900XTs