It would probably be best to wait for the new cards to come out and see what they offer to the table. I'm a bit surprised to see you wanting to upgrade from a 7850 are you not happy with its performance? Are you wanting to max things out?
Either a 7950 from amd or a 660 ti from nvidia, or wait for newer generation cards, which there's not a date for both sides, it all depends on what performance you're expecting, if you feel that the 7850 isn't cutting for the games you play, you might get a better card.
Hmm, I don't think its a good value to upgrade from your card at this point. You invested in a card that is a current generation card so that is where my logic is going. Normally people upgrade once every 2-3 generation of cards. If the next series blows this one away and you are wanting a upgrade that could be a option otherwise I'd just sit tight and wait for your card to no longer be up to snub in the games you play.