But the 77--'s are weaker and cost less than the 6850.
That's the point, DUH. They're weaker, or course they'll cost less. But HD 6850 doesn't cost THAT much more, and it performs much MUCH better.
If you can afford it - buy Gigabyte's HD 6850 without any hesitation, you won't regret it even one bit. If you can't afford it - get cheapest HD 7770.
Anyway, it's for you to decide in the end, I just really hope that you will make a truly wise choice.
That's my last word on it.
Have a nice day/night, and I wish you the best of results in any of your doings. Peace.