I find 38 meters and 30cm keeps my ground textures (trees, houses, shrubbery?) sharp. I also fly at .30 zoom levels all the time which I think keeps textures sharper and perspective seems more realistic to my eyes. I up the mesh detail to 19 or 10 when flying mountanous areas or something like the Grand Canyon. Death Valley, Bonneville Salt flats, large bodies of water...38 is probably overkill, LOL.
I also think when flying areas with lots of houses, trees, and other objects the mesh detail is less important/noticeable (unless t's a leveled house on steeply sloped ground, attached to it on one side only and this seems to be exacerbated by higher detailed mesh). But in mountanous areas (say the Alps) where the ground terrain itself is the predominant visual aspect the higher the mesh detail the more satisfying it is to me.