If so, then the 4850 1GB. If you were upgrading your card for 2 or 3 years, i would have suggested 5770. But, if you do another graphics card upgrade next year, there is no point adding a $55 + for just 1 year
They are both good deals at their price so really it depends on what you want to spend.
The HD4850 will be good for your resolution while the HD5770 will be great and offers much greater power efficiency and DX11.
One thing to consider is that the HD5770 scales very well in crossfire and the low heat/power aspect makes it a rather painless setup compared to the old hotter, power hungry cards. You could get an HD5770 now and grab another when you feel the need and prices have come down. 2 will give you performance similar to an HD5870.
Good luck , its a tough call. LOL
I used the reasoning , I couldn't justify the extra money (when building my rig and choosing the cheaper alternative, in my case a 4770) to significant other. After making the leap for a small ssd,i5 750 etc. And I didn't want to butcher a working computer to stretch the purchases. Time old catch 22's !!
Good Luck !