Yes, resolution does affect how a card performs. You can run at lowest resolution and have all settings on high, or run at highest resolution with lowest settings.
I'd say a 7800GT should be able to take most games at 1280x1024 at max settings. My 6800GT AGP with 2GB of ram can take BF2 at 1280x1024 at max settings except for 2-3 medium settings and NO AA, so I'd say the 7800GT can go fully max with 4xAA.
The 6800GS should be good for 1024x768 with mainly max settings without AA, but the 6800GT should be bale to perform 1024x768 at max with AA.
So to summarize:
1280x1024 Max Settings 4xAA: 7800GT
1280x1024 Semi-max settings No AA: 6800GTw/2GB of ram
1280x1024 Medium settings No AA: 6800GTw/1GB of ram
1024x768: Max settings 4xAA: 6800GT
1024x768 Semi-max settings No AA/2xAA: 6800GS
If you're talking about upgrading from the 6600 in your sig then the GS is a pretty marginal step up. Of course you'll recoup a larger percentage of the GS cost if you sell the 6600, but IMHO I would either step up to the 7800 series or hold out till the price drops or the next gen is released.
Get the 7800gt, its more future proof and will provide a better boost in performance when going from a 6600...
newegg has evga 7800s for a great deal:
evga 515 7800gt - $304
-20 dollar MIR
-20 dollar instant rebate (promo code evgacpl)
= 264 dollars for a fantastic card
If you have the money, get the 7800GT. Best price to performance ratio. If you are benching and want top scores go with the GTX512 line, but you are gonna need alot of CPU, and it's not available yet, so you'll be basically buying for the future and gambling that they won't come out with a better card. Personally I wouldn't take that gamble. hehe I'd go with the GT if I were upgrading right now.
so the lower the resolution the higher you can run your settings correct? I thought it was that way, but wont that bottleneck your cpu? Oh yeah newegg has the evga 7800gt for 299 now. i am about to jump all over that.
the GT will do great for you cre8, im sure you will enjoy it.
read my post above on how to get a evga 7800gt for $264. When you have the lower resolution your cpu becomes the bottleneck, but when you raise the settings the GPU has to work harder (therefore lessening the bottleneck).
I'd also go with the 7800GT, I'm running a GTX at 1280x1024 and I have no regrets. Although the 6800GS is cheaper, the 7800GT will pay for itself in the longrun since it will be able to play new games longer.