Just purchased and downloaded from the link on itch.io (V107)
I wonder if the performance issue is related to NVidia cards? I know there's at least one other game I've purchased recently that has similar issues.
I have a performance issue even in the initial menus where you pick your character and difficulty level.
Win 10 pro x64, all updates applied.
Intel i7 940 @ 2.93 Ghz
MSI NVidia 970
Here's a short video capture:
Overall, much better gaming experience.