I just did the math on the 7890 vs the 7870 based on Avg FPS of a Dozen current games, and the conservative assumption that the 7890 will deliver 10% more net avg FPS than the 7870. the 7890 would have to price under $205 to provide a better $:FPS value than the 7870 you can get at $185, and we all know that's not going to happen. for the 7890 to compete with the 660ti it has to be price below $265 in terms of $:FPS value, which means a lot of recent factory over clocked 7870's still selling around $250 will have to fall a lot in price to make room for the 7890.
so my educated guess is the high end 7870 cards will fall in price,
but not much else will change on 7950 or 660/660ti card pricing.
I would also state if the 7890 card is sold over $275 it will fail
as the far lower power consuming 660ti will be a better value.
FYI: my "price" is net cost in the open market, not MSRP nonsense.