I heard awhile ago some people on these forums talking about the "2 Gen" rule. I don't remember if they were talking about CPU's or GPU's (seems relevant to both) and it seems very relevant in this situation.
For instance, my 6850 is, as of right now, 1 generation old. It was replaced by the 7850 (obviously). Is there a performance increase? Yep. Does the performance increase justify the nearly $250-$300 price tag the 7850 had when it came out? No.
Now if the Radeon 8850 comes out and is, let's say 20% faster than the 7850 which would make it, lets say 50% faster than the 6850 (2nd Generation rule) then would the $300 price tag (speculation) be justified? In my opinion, yes.