you need that much GPU for WOW? I thought WOW was CPU dependant not GPU so much.
To an extent, it is CPU intensive, but in heavily-populated areas, having the graphics up will slow down any system with a less-than-capable graphics card. Mind that you don't NEED that much GPU power, but I am assuming (forgive me if I'm wrong) that you'd want a GPU that can keep up with the 1100T in all respects.
And again, I'm giving you advice based on the fact that you said "best graphics card" for WoW, and assuming you're playing other stuff occasionally. For your system, you're only limiting yourself by getting a weaker last-gen GPU like the 5770; that's not to say that it's bad for the price, but if you get that now you'll probably find yourself underwhelmed by the difference (or lack thereof)
from the 4850. Now look at the difference between the 5770 and 6850
. Unfortunately, I can't do a direct comparison, but the 6850 blows the 4850 away while the 5770 just kind of shoves it aside a bit. Of course, the 6870 then trumps the 6850 for a mere $30ish more (and a Crossfired 6870 configuration is one of the best values ATM, if you want to Crossfire down the road).