if you have Vsync (or whtaever the ATI equivelant is) on you should stay around 60, if not then i couldn't tell you really.
If i upgrade my video card to Radeon 4890 can my powersupply be enough power for the video card? or should i get radeon 5770?
A BFG 550? I don't know the specs on it. You may want to google "power supply tiers". Your going to have to compare the power consumption of the video card you choose with the amount of 12v power, how many rails, and MOST IMPORTANTLY, the amperage that the power supply provides.
LAWLZ~ can you help me?.. Can you help me find out which video card will be good enough with that powersupply?