I was talking to someone online last night that also was experiencing issues and recommended it to him and it helped a lot too so thought I'd share it.
Set GPU/CPU Synchro to "NONE" in settings - advanced - compatibility
Also the ingame vsync in compatibility seems to be buggy.
I was mostly solid 60, but occasionally online it would drop to 40.
Disabled vsync and it was solid 100 and where it dropped to 40, was now dropping to 80.
So I forced vsync on the card instead and seems to have sorted it for me.
Solid 60 now pretty much all the time, and lowest I've seen it drop to is 56.
Hope these settings help some folks
Mark.