Comments - FelisNoctu

For the people wondering, Xaphan mentioned on the Phrozen Keep forums that they're currently busy with full time work as well as their education, but they haven't given up on the mod. They've just had to adjust their plans for release.

Options -> System -> Advanced -> View/Camera Effects = No

Doing this disables almost all, if not entirely all, of Sikkmod's visual effects. That's why your FPS goes up. Good if you just want all the model/texture/particle/gameplay changes though!

If you want to keep Sikkmod's graphical changes on, the biggest drains on your performance are going to be Soft Shadows, SSAO, and Sun Shafts (under Sun FX). Making sure all of those are off should result in a huge boost. My GTX 1080 drops from 60fps to about 32 if all of those are on, each one's worth about 10fps for me at the landing pad at the very start of the game.