As the title says, with vsync and immersive railroading installed, the fps go from 60 to 30.
Without vsync, it drops about 10 fps from about 80 to 70

I am having trouble reproducing, what GFX card do you have?

R9 200 Series.
R9 280x specifically.
My brother has a GTX 960 and he has the same problems with vsync.

I should drop in my R9380 and give it a test

I'm noticing the same on the temporary system I am using (as my main system is in for repairs [bad power socket]). This one has Intel HD Integrated Graphics.

I've improved the rendering system significantly over the past few updates. I am going to close this for now, feel free to re-open if you are still experiencing the issue