well i was using a 5870 till it fried. i am ordering a R5870 lightning from msi and going to OC it to 1ghz core, hopefully 1.2ghz core and 1300 memory. and a 460 is perfect for a physx card for modern physX games. with my 9600xxx as a physx card in games like Metro 2033 and mafia II is used 100% and is still not enough. a overclockable 460 like an EVGA card (a perfect on all levels OC card for Nvidia), would make a GREAT physX card, and would be future proof. at stock clocks it would be just a little tiny bit more than i will need, and as physx apps become more intensive i can OC the piss out of this thing to get what i want.
when i was using my 470 as a dedicated physx card it was using 60% of the card most of the time in metro 2033 and it jumped to 80% on a few occasions.