Im having pretty much the same issue. Except last night (and ever since the release) I was running at a constant 60 fps with vsync. Just now I run the launcher, it patches as it often does, and bam 25 fps.
Tweaking settings in nvidia changes almost nothing, and changing ingame settings does nothing significant. The problem is the games resource usage. My gpu maxed out at 63%, my CPU was at 68%ish, and the game was using 1GB RAM at its peak, compared to its usual near 100% use and 1.7GB of RAM.
Any suggestions? Or is this a wait until they fix it thing?