one more point I thought I should make as the OP on this topic...
Whether the DX10 Fixer works for you or doesn't - is not on Steve - he is just working around and through all the broken schtuff MS left in their wake when they rushed to publish FSX...all unfinished, as it were.
DX9 worked well enough for me and I had had my fill of tweaking and tweaking and tweaking FSX to make it so - believe me - I didn't really want to "start over" with DX10....However -
With all the guides available, mostly hosted right here at SOH, and with some assistance from other forum members, I am glad I made the switch to DX10 - and I guess I'm lucky that it works for my rig.
I can see not wanting to lay out the cash upfront in the hope it will work, so if DX10 preview (without the fixer) doesn't give you increased frame rates over DX9 then there is probably no reason to take the risk.
But test it this way - select a default aircraft (Cessna 172) - set all scenery sliders to the halfway mark (not trying to win a pageant here - set the in-game FPS controller to "unlimited" - select KORS Orcas Island for the takeoff - and select fair weather midday - fly it once in DX9 and then in DX10 preview with the FPS counter running and see for certain
whether your FPS are consistently higher or lower in the preview mode...
When I finally tested it this way I was shocked at how fluid the movements were, panning the camera in the VC and the glassy smoothness of the flyby views in the Preview mode compared to the DX9 mode- which- even at the reduced settings I outlined above showed some chop and stutter