Strangely enough, I only saw major framerate drops during combat even when nothing was happening (I only started noticing them in the Dark Forest, but it may have started happening earlier). It's like exploration is at 60 fps (with v-sync) but the moment combat starts the framerate drops.
Yeah combat mode does seem more demanding, I'll go from 60 into the 50's when combat starts up.
But our problem is that we've experienced that lower rate persisting after combat and actually getting progressively lower afterwards and getting tied into the save somehow, almost as if there's some errant loop jamming up the cpu or gpu.
I'm happy to report I've yet to see the issue reoccur several hours after backing up to a clean save but I'm ever watchful, - the issue is out there.
