Well let's think futuristically...
Within the next 2 years, do you plan on only playing Aces High 95% of the time? Do you own or play any other games right now?
If you're that big of a AH junky and life does not exist outside of it, I'd proably would stick the 3850 in there if you want to upgrade/replace that card.
Otherwise, the 4850 seem to be dymo and crossfire would help with high end games playing at large resolutions.