It is not really a huge jump over the 6770. The 7750 is about on par with the 6770, but it really varies depending on the game.
I see the cheapest 7770 at $120 on newegg and the cheapest 6770 at $80, not taking into account rebates. The 7770 is in no way worth $40 more than 6770.
Of course the 7770 is I believe DX11.1 compliant, but I doubt that will ever matter. Probably at the most it will make about as much difference as DX10.1 made for the HD3k/4k Radeons i.e. not much at all.