If you look at the early benchmarks and reviewer remarks you have to wonder if DX10 will really deliver as promised? The key word is EARLY in these reviews.
There is still a lot of work to be done in drivers and code bases, but a bolt on solution that MS plans for FSX is less than promising.
FSX64 (my predicted name) will make good uses from the ground up of multicores and DX10 but until then, patch is just what it is.
Time for me to go out and get a cheap highspeed DX9 card for less than $200. ATI X1950XT for $199 at Newegg.