+1 on Ileader36's comments. Yes, you can use the HD4850 but the board just won't allow you to use it at full potential. First, the 4x somehow limits its oc capability. I was stuck at 625/993, maybe push it to 650/993 but it just wasn't stable. Had to keep it at 625/993. Also, as soon as I put in the HD4850, I cannot overclock the E5200 more that 266fsb (which btw, was done using BSEL). Before the HD4850, I was able to do 280x12.5 no problem.
Ileader36: I got the SD964 when I switched boards but now with the UD3P and E5200 oc'd to 333x11 (even 360x10 at one point), my idle temps were 32-33C and load temps running Orthos/OCCT were 54-55C while IBT had it up to 59-60C, all these with an ambient of 70F or 21C. I do have the Xigmatek Crossbox backplate too.