What resolution will you be running at? At something like 1280x1024 it might be overkill but at 1680x1050 and above it would be able to work to its full ability. You should be easily able to max everything out, but you will need a new PSU prior to upgrading it.
oh, i'm forget about his psu...
If u want 5850 then u must upgrade your psu to better one, like Corsair, OCZ, Antec, PCP&C,ect...
5850 is directx 11 and eyefinity might good for future, which 48xx series doesn't have it...
yes i would definitely need to buy new PSU but i not sure about buying 5850 since there's no fermi nvidia cards on the market to drop the price and in my country it cost around 400$
and decent corsair 550W is around 150 $
so now i aim at hd 5770 because 400w psu can run it but again how long 5770 will hold out playing games on 1680*1050 with decent details and will it be enough to run dx11 games?
I am running 5850 on a 400W power supply but I am at the very edge
Even slightly overclocking my GPU or CPU is resulting in shutdown and power supply protection kick in. I am upgrading as soon as possible. However I LOVE the 5850
So, putting 650 $ in old rig is not so wise, since testing machine on this review http://www.pcgameshardware.com/aid,700050/Dirt-2-benchm... is quite faster than mine and it struggles with 5770 on 1680*1050 but again 4800 series need more power than hd5700 series and seeing this review I'm quite confused about my GPU upgrade