We all ask the same questions about waiting when making a purchase.
The 6850 barely squeaks out over the 7770 at a much lower price.
The main draw with the 7770 is the turbo low power requirements as well as better dx11 support.
The 6850 however is low on requirements itself and also supports dx9 and 10 better currently so the broader range of games out will play better on it.
If i had this choice i would be getting the 6850. The 7770 is just too high on price right now to make the power requirement worth the price over the 6850
heres the Tom's review with direct comparisons of the two cardshttp://www.tomshardware.com/reviews/radeon-hd-7770-7750-benchmark,3135.html