i have a an XFX readeon HD 5850 Black edition, and i run all my games at 1920x1080 and maxed out with all the AA possible, so far i haven't found a game i cant play at those settings. Crysis warhead gets around 25 fps, 4x AA, 1920x1080 and all maxed out...but its very playable for me. with 8x AA its still playable but there a lots of parts where it drops down to 16 or so and it gets annoying so i leave it at 4x AA
Physx basically adds small details like fabrics tearing and makes small particles like pebbles falling, sparks, water flowing more realistic, its not a HUGE difference though on most of the current games out that have it, but its kinda nice
i tried running the game with physx on my HD 5850 but it starting lagging badly on a certain part where windows were getting shattered, but turns out im not the only one who's getting this prob, and to fix it im getting my friends Nvidia graphics card and just using it as physx card only, so that my 5850 can concentrate on everything else.
With the i5 @ 3.2GHz you are limited only by your budget and what you can put in your motherboard (which is 2 cards running at 8X or one running @16X). If you want a bargain and don't mind not having DX11 2x radeon 4850 4870 or 4890s can still be found at bargain prices if you look around otherwise look at Radeon 5770 5830 5850 or 5870 or even 2 x 5770 or 5830. The new Nvidia 260 is also worth considering. Cards above these are most likely overkill but if you have the cash burning a whole in your pocket go wild.
Simon, your confusing the Original Post(er) with the first replier. We have no idea what his system is other then its "stacked".
Lava, I would shoot for something like the GTX470/5850 or even the 5870 if you don't feel like up grading for awhile. The GTX460/5830 and 5770 can work in a pinch, but you won't be able to max out things all the time.
dude get a gtx 460 there your best bet for high resolution gaming! the new fermi chips are amazing, adn the card is super efficient. I play at the same resolution as you and the card keeps a steady 3 fps on cryisis and bfbc2. It is the best card out for the price and i highly recomend it!!!!!