Oh, my - well, let's see -
I've got practically no add-on airports in my FSX so just about every flight starts at a stock airport.
I haven't gone back to DX9 yet, as so far the only other issue I'm getting from DX10 is a sort of "shimmering" effect from some runway surfaces, where it seems to flicker between being there and not being there, very rapidly. It seems the benefits of DX10, at least on my setup, so far seem to outweigh the disadvantages.
I haven't added anything yet to try to counteract these issues yet, but the kindly-provided links to the fixers will be tried and I will report results.
PS - I haven't noted any frame rate drops yet from being around clouds but will check on it.