Doom3 Graphics Cards - GPU performance or video memory?

Does anyone here have any insight into graphics card hardware for Doom3?

I have a budget of about 100-120GBP for a new graphics card, my sole intention is to get a better framerate and display quality over my current GeForce MX420 64MB card.

In various places where I've been reading, mention has been made of Doom3's potential to exploit video memory. As a result, I don't know whether to go for a slower card with more video memory or a faster card with less.

The cards I've been looking at are based upon the nVidia 5700LE (256MB) and nVidia 5900XT (128MB) chipsets.

Can anyone offer any insight into the potential display quality versus framerate tradeoffs between these two cards? Also, perhaps I'm barking completely up the wrong tree here; considering my budget, what other card(s) should I be looking at? Faint memories of ATI owners and their card's driver problems are steering me away from that brand but perhaps I should consider those too?

[I know that perhaps there are probably a dozen other places where I should take this post but I respect the people and their knowledge on this board more than other places.]

i don't like either gf card youre selecting. they're both cutting performance
go with either the 5700 ultra or a 5900 non-xt. not sure what the pricing is on those, though
xt & le mean bad stuff in nvidia

If I had it to do over again, I'd buy an ATI card instead of an Nvidia card.

I finally got a set of Nvidia drivers that didn't have the "slow smoke" bug and had fast performance, but they crash in Far Cry and Halo. In order to run either of those games, I have to rewind to older drivers that slow down with smoke effects.

I don't understand why Nvidia can't put out a set of drivers that simply works for everything. I thought that was the whole point of drivers.

Not that it helps you much, but I've only got a GeForce FX 5600 128MB and it runs Doom III at 800x600, Medium Qualtiy, with everything but AA turned on at a very decent framerate.

Quote:
i don't like either gf card youre selecting. they're both cutting performance
go with either the 5700 ultra or a 5900 non-xt. not sure what the pricing is on those, though
xt & le mean bad stuff in nvidia

Thanks, I didn't know that.

Upon reflection, I think it's down to my budget that I'm looking at XT/LE cards. I'm consciously not spending much here (for reasons that I won't bore you with) and the alternative chipsets appear to be the Ultra versions that are simply outside of my budget