I have Radeon HD6770 along with Intel E8500 and 2 gigs of RAM.
Windows 7 installed with latest AMD drivers.
Average FPS on maximum settings is below 55, so enabling vsync won't be very wise.

When I enter location full of mobs, the screen freezes for a second, and after I gain control again my character is already hit a few times.
It became especially bad on nightmare difficulty where packs of enemy are bigger and they use all kinds of spells.

I cannot set video quality settings to low because 60" plasma demands highest picture quality possible.

So what should I do to achieve good performance level?

Upgrading the RAM is the easiest thing.
I could also return the new HD6770 and get HD7700, if that would be of any help.

Or maybe there is some bugfix upgrade from Blizzard or AMD on the way and performance issue will be adressed without my interference?