If the XFX really has only 533MHz memory clock, stay away.
Personally, I would buy the Leadtek, because I hava a Leadtek A6600GT now and I'm satisfied with how it worked until now. Also, the cooler on it looks nicer than the MSI's. If it's the same one as on my 6600GT (it certainly looks like it is), I can tell you it is quite silent.
But, if I were you, I would first check the manufacture's site for all 3 cards, because I'm sure you can find more details on the cards that way.
(I think the 533MHz on the XFX could be a typo).
had a geforce 4 from leadtek,
massive cooled card, never had problems
switched for a 4600 (no leadtek) and needed to upgrade cooling to a zalman to eliminate noise.
also a TV-tuner card from leadtek (bad driver-support) plug & problems, windows doesn't recognize the card, must install driver manually, and windows warns you it can't determine if the drivers are specially for the card,
once installed, the TV-suite software doesn't recognise the card ans won't play. so currently i'm forced using 3th party software. which runs perfectly (ChrisTV).
but overall, leadtek makes great hardware, and the driver support for you're card shouldn't be a problem, because leadtek is not in charge of the drivers, Nvidia is!
Would but to switch over to PCIE would at the minimum cost me another 50-60 bucks(difference between teh GS and GT options for me whether the GT is AGP or PCIE the difference is basically the same). Guess I would be able to move the GT over to a newer system later on, but wondering how fast say DX10 could make it obsolete. Trying to squeeze another year or so out of my current rig before I do a full system rebuild.
In any case exploring all options right now though its looking like either the 7600GS or 7600GT just a matter of how the budget falls in the end.
Is a possibility.. though I'm upgrading a Radeon 9600(non pro) and while I know it was one of the buggiest cards ATI ever released driver wise it(took about a year to get some revisions to fix some bugs in games when running certain features it was supposed to do like shiny water) has me kinda weary to go wtih them again. Card either seemed to work really well.. or not perform to its level depending on the game. My brother's 9000 never had the same problems and performed well for its price range.
But if I do give them a second shot...
x850 pro doesn't have Pixel Shader 3.0. Won't this hurt me if I say try to play Neverwinter Nights 2, or BF2142? And doesn't FEAR use it as well?
I figure it wont' cut say Bioshock and will definately have to upgrade to play it by then right?