While playing 0.50 with some command-line fixes in the game shortcut my game ran about 40-50fps.
After the update to 0.51 i hardly get 8-9fps

This is the commandlines i use:
-noSplash -noPause -cpuCount=2 -exThreads=3 -maxMem =8192

I've tried removine the -maxMem function and alter both the CPU count and threads, but still the same result.

However, the ingame menu/ start screen menu, will show anything between 18 -38fps depending on my settings.

I run this on a MSI Z87-G45 with 8GB Ram, i3-4130 CPU and a GTX 750