Using the latest SKSE 1.04.02 and followed the instructions to a tee.
I didn't get the 5-10fps like people are saying. But I applaud the modders for trying.
The 40% performance gain is there, it's just on your system you can't see it. If you have ~30 FPS stable then it could be Vsync interfering. If you have <30 then it's probably another bottleneck. If you already had 50+ without the mod at the trouble spots then you didn't really have much of a bottleneck to begin with.
Remember: 40% performance gain when doing X does not mean your
framerate will increase by 40%. It'll only increase if X is actually a bottleneck for your system.
Edit: Also some people are saying they need to go to places like Markath and Riverwood, which are the most famous FPS killer towns, to see the difference (especially with Markath).