Any idea as to how to improve the framerate without decreasing graphical quality? I get about 80 FPS steady in vanilla, but about 20 in Nehrim (even the interiors!).
I also have performance problems in Nehrim and I don't think there is a way to get even close to vanilla performance without a substantial loss of visual quality. There are simply too many objects and NPCs at once. Have you been to one of the big towns yet? My game became almost a slide show in some town areas. In vanilla I get a constant (capped by Stutter Remover) framerate of 55 (with ~100 mods, many of them very large and complex), in Nehrim the framerate hovers between 10 (some town and other heavy performance areas) and 40 (average forest away from the crowded streets). Not counting interiors, of course a small interior with only one or two NPCs gives a great framerate. It is playable as the framerate is ~30 most of the time, but after getting used to my 55 FPS it feels a bit sluggish.
The only tweak I know of that gives a slight performance boost without decreasing visual quality is to change these settings in the ini:
uGridDistantTreeRange=15
uGridDistantCount=25
In Nehrim you can't see very far usually and it has lots of VWD objects (much more than vanilla for sure). I set mine to 15/15, which is enough imo and gave a small performance boost.
Maybe Low Poly Grass might help as well, just not sure whether they use custom grass types.