If you don't want to fiddle with it, get CM and shader patch, turn off the WeatherFX, extra lights etc in shader patch (I don't know if you also have to manually turn off light configs/vao patches autodownloading. basically you can turn off anything you don't want to mess with) and you have the base game appearance but with a bunch of cpu/gpu optimizations.
OT:Even when not running sol, using lighting fx is a great improvement to visuals. Dynamic ambient will cause the car interior to match the exterior light tone near 8h or 18h, instead of looking the same as at 12h and completely mismatched/out of place. Also, on tight tracks like Norising, the exaust flames flashing on the walls adds a lot to ambience, or illuminating dark car rears under big spoilers as with Group 5s.
Right now, too keep it more vanilla looking, or according to track makers view, it's also preferable to disable "add reflections to roads" under track enhancements. It can mess the track under some combinations (see example
here).
@Fat-Alfie, if you try a later version (such as current p129), fps improvements will be much greater than what you're experiencing now due to newer cpu optimizations. I went from 14 to 19 AI with slightly better fps on starts, around a 35% fps bench increase without sol, and 25% with 1.2 (vs p74) with on an old fx8350@4.4 that replaced another excedingly old PhII@4.1 on my sec. system. On older versions like p49 and p74 you'll *still have a slight boost vs vanilla with csp on single car grids because the two default cpu optimizations, mostly for deduplicate meshes (is noticeable on a old cpu like mine on grid starts).
Regarding VAO, at least on feldbergring, the last time I checked it (might not be valid anymore, tough) was only affecting a few objects away from track and under trees, it didn't seem excedingly invasive of your artistic view, but it's perfectly understandable that you'd prefer none of it.
The greatest change was on Thomson Road, where all the base of track side vegetation is darkened. In some places it really helps to blend the 2d vegetation better, while on others it can look overdone, specially over some larger objects you've already AO'd (some wooden grandstands, etc). The Shaders Patch Debug app makes it easy to check, but it'd be nice if CSP had a main switch under options to toggle VAO.