Thank you for the GPU tweaks, VonS. I'll certainly test them out, at least once I get a chance to actually do a little flying!
In regard to matching the graphics detail in the various "rings" I think you will find that the outer most ring is the most problematical. Trying to match the graphical detail in the outer ring with the inner rings will definitely result in the largest fps hit AND most likely an increase in stutters (the longer kind, not the micro-stutters that you also referred to). In my experience helping PR with the blue triangles mod, I noticed a fairly predictable stutter occuring when the terrain detail in the outer ring is updated, particularly when the terrain transitions from generic to detailed terrain. In fact, increasing the object density in the outer ring too much can bring the game to a crawl and even cause a game crash.
Of course, if you are referring to the inner and middle rings only, then this is not as big of a problem.