in Far Cry 2 the 6850 gets 15fps more than the 7770 @ 1920x1200 HQ 8xAA etc
without checking more, I think I remember seeing the 7770 getting beat out in almost everything - is a strange card, seems to exist more for marketing purposes than any real practical use in my mind... People like newer numbers + just plain confusing for people not wanting to jump into lots of benchmarks etc
I would stick with what you have a while longer and upgrade 1st Quarter next year once price drops come from the new 8000 series cards + maybe OC your card to 6870 speeds + for now if you want more speed - The gains from such an OC are good, maybe an extra 7fps+ ...enough to get your smooth back ^^
No worries if you can upgrade anyways right?
Or you know what to go with if you wanna spend cash Now