Which card? (Both XFX)

Ive been going over this in my mind several times and looking over different sites for comparison, but here is my question: Which one would be more suitable for my system: the 7900GS 450/1320 (256mb) agp or the 7950gt 550/1300 (512mb) agp? Here is my system config:

Pentium 4 (Northwood - Socket 478) 2.8GHz (FSB = 533MHz L2 Cache = 512k)

Memory = 2GB PC2700

Two Hard Drives (120 GB each - 7200rpm)

450 W Antec Smartpower 2.0 PSU (32A on dual 12V rails)

one 80mm Vantec Tornado 5700rpm case fan

Motherboard is the Intel D845GRG Micro ATX

Right now I have a Geforce 6600 GT (128MB) Dual DVI with two LCDs... Viewsonic 20 inch (1600 by 1200) and 19 inch (1280 by 1024) I will be using the 19 inch for my gaming and 3D work.

The reason I cant decide between the two cards is the memory issue. Ive heard that games like Oblivion, GRAW, Quake 4 and Half Life 2 can make use of the 512mb of the 7950GT for high res textures (there are mods for Oblivion that implement this) and there is an "Ultra Quality" mode in some of the games that requires 512MB video memory - even at 1280 by 1024 resolution. Also, there are newer games coming out (Crysis, Bioshock) that might need the extra VRAM in high quality modes.

Ive also noticed that reviews of the 7950GT agp on newegg have gotten better recently (newer version of the card?) so that is another positive in favor of that card.

Here is what's in favor of the 7900GS agp. Using a Pentium 4 2.8GHz with PC2700 memory would I even be able to utilize the high res textures in those games or would my cpu slow me down and bottleneck the 7950GT and would the extra VRAM be wasted? One thing I forgot to mention is that I have an AGP 4x port on my computer-- would that affect high resolution textures if I do go for the 7950GT ? Also, will newer games use up more bandwidth, more than my 4x port can provide, thus wasting the 512MB vram ?

Another thing I havent mentioned yet is that my case runs pretty hot (thats why Im adding a Vantec Tornado case fan - despite the noise, they have a good rep of reducing temps by up to 10C). Even with my 6600GT in there right now, GPU temps are over 60C at idle (!) and during testing (such as 3DMark) theyve gotten up to 100C. I dont notice artifacting even at 100C, so there's at least one positive. I think the 7950GT runs hotter than the 7900GS but Im not sure about this. Hopefully my new case fan will help lower temps somewhat.

Anyway, that's my situation in a nutshell. Which one do you guys think purchase? The 7950GT is 70 dollars more than the 7900GS so it's not much of a difference, but would my system be able to utilize the full capabilities of the 7950GT (i.e.- 512mb VRAM ?) even with a 2.8GHz P4, PC2700 memory and an AGP 4x port?