Digital Foundry had a go with the PS4 version and they said the majority is 30fps rock....steady. That can't be said for the PC port. I see people in this thread with 980s and whatnot and they still experience these massive frame-drops.
It's been mentioned already, but it seems like the DRM is the prime suspect with a lot of these issues. Wouldn't be surprised if they patch it out in a few weeks. Or sooner.