i still would get a 5850 if your going to overclock compare them both overclocked an overclocked 5850 is as faster then a stock 5870 so as i said if your going to overclock the 460 also look at the 5850 when overclocked
not to mention the 5850 still uses LESS power then a 460
physx is nice if u must have it get a 460 but fact is only 14 games released use physx on the gpu and of them only 1 really needs it to be playable and thats Cryostasis total games using HARDWARE accelerated Physx total with games released and in development is 24 total out of 1000s of games.
That said the 460 is very attractive card at that price but id still take proven performance and lower power consumption any day
and at stock the 5850 is also quieter which is a bonus for me