I have a 7600GT and it plays Doom3 on the default high settings just fine. I would assume the GS would do well, too.
Have you played it yet on your system? I don't consider myself in expert, but with that cpu don't you think you might run into some trouble?
Minimum:
P4 1.5Ghz CPU (or equivalent).
384MB of RAM.
64MB graphics card (see below for chip details).
2GB of free hard drive space.
Supported cards:
GF 4 MX.
GF 3.
GF 4.
GF FX (and higher).
Radeon 8500s, 9000s and higher.
PC Gamer were the first to review they themselves recommend:
2Ghz CPU.
512MB RAM.
Radeon 9800.
5-channel sound card and speakers.
I have the GS and I can play Doom 3 on Ultra Settings without any troubles.
If you can afford it get the 7600GT it should run most games on high settings i can play fear maxed out at 1152X1200 or something cant remember the exact resolution but it plays it with 20-80 FPS so it should play doom just fine.
By "maxed out" do you mean full AA and AF or just all high settings?