HD4850's are going well cheap now so i'd just get another & crossfire it with the one you have. Will save you a packet over shelling out on 2x HD5770's.
Maybe get the 2 HD5770's sometime next year when their abit cheaper & theres some DX11 games out.
Dr emulatorhey whats wrong with gettin another case ?
Yeah or another case & a HD5850 !