I disagree that the 650 Ti will be closer to the 7850 than the 7770. It'll be much like the situation with the 660 Ti, only worse. The 660 Ti has the same core count and clock speed as the 670. The 670 general
beats or ties the Radeon HD 7950 at stock speeds. Chop out a portion of the memory bandwidth from the 670 to make the 660 Ti, and
some of those advantages disappear. What's more, the 7870 is competitive with the 660 Ti
in a fair amount of games, even beating it sometimes. With the 650 Ti, they're both cutting the core count down from the 660 GTX and lobotomizing the memory bandwidth to an even greater extent than between the 670 and 660 Ti. We've got a repeat of the situation with the 660 Ti or worse, calling it now.
As for the 6790 -- the 7770 has better tessellation than both the 5770 and 6790. Stepping up from the 5770 to a 6790 in comparison to the 7770 should not be enough change the winner if the deciding factor is tessellation. Memory bandwidth has to be the source of the issue. Don't get me wrong, the 650 Ti is going to be faster in games that aren't memory constrained, but in games that are it's going to hit a wall and hit it hard.