If you search for "FSX.cfg" then edit the "TEXTURE_BANDWIDTH_MULT" from like 40 to 400 (found this tip at SimHQ.com) then FPS actually gets better, if not the slowdown/speedup problem is resolved. It may vary, as I fly the KBT Super Hornet and get great FPS, while the Abacus F/A-18E I've seen a little more of an FPS hit, so it may be just model quality, not sure. But give that a shot and it may help, and this is with SP1