err you made two threads.... lol
if your going to upgrade to HD4870 wouldn't it make senses just to get the HD4870 anyway? than add another later
and for GTA4 you may want a nvida card but I managed with a single HD4870 with meduim that was maxed btw it played nice. means you can have corrsfire if you want the equivnent to say two HD4870 in nvida form you would be looking ath the GTX285 or GTX295....annoyingly GTX275 is about the same as the HD4890 so about %10 faster
Since i dont got much money at the moment ill get the HD 4870 512mb and crossfire later
and what did u mean when you said "with meduim that was maxed "?