Very bad perfomance in fsx with high end pc, help!

Hey, last year i got a high end pc for 2500 euros, and im getting really bad performance in fsx, here are the specs:
Nvidia nforce 780i Sli
intel core 2 quad q9550 runnin at stock 2,83ghz, liquid cooled
2x nvidia 9800 gtx in sli oced to 760/1885/1150
8 gig ram ddr2-800/1066 dual channel
vista home premium 64
Psu 750w
samsung syncmaster t220 tft 22 inch
ok, so no matters at which settings im runnin the game, low, ultra high, i never get over 20 fps, the fps locker is set at 60, i also tried unlimited fps lock. Im runin 1680x1050, but i also tried 640 res and no fps increase. I checked the cpu usage and mem usage and just 1st core is used 60-70%, other ones are at 5-10%. Mem usage in desktop at idle is around 1.5 gigs, mem usage in fsx is 2 gigs. I applied sp1 and sp2, tried also reinstalling fsx and reapply the pathes. I know that fsx dont support sli,so i turn single gpu mode.When i try using sli, the game run as same as b4. The gp1, is at 55-60º when playin fsx, the same as in idle.I also tried enabling dx10 mode, but i get the same bad performance and runways and shadows makes like flashing. Whats the problem? All other games such as crysis, gta 4, cod4, cs:source, left4 dead, fallout 3 got excellent frame rates, never under 35fps. For example, in crysis i hav 41-45 fps in benchmark at ultra high. I read problems of other persons, with quad cores xtreme, gtx 280, gtx 295, gx2s, having the same bad performance than me. I hav gpu and mobo drivers updated. Please help me, i dont wanna play fs2004 forever, fsx is the latest on the series, microsoft cancelled flight sim series

Honestly if it's only that one game, sometimes it just happens. Far Cry 2 won't recognized SLI on my system, whether I use 2 280s or 1 295. I've got no problems with other apps, it's just that one game. Other people with inferior set ups get better fps than me. Doesn't matter what drivers I use, it just doesn't like my machine. One of the mysteries of PC gaming.

its a cpu intensive game, if you want to improve performance then you'll have to oc that cpu. they recommend themselves that u have a cpu @3.6ghz so i'd at least try an oc over 3.0-3.2ghz. make sure you install fsx sp2 aswell from microsoft.