I agree with Launchbury and cyberstudio. You need more CPU speed and at least a 512mb video card. I am running:

* WinXP Home SP3 * INTEL Core™ 2 Duo E8400 3.0GHz oc'd @ 3.85 GHz * ASUS Maximus Formula Intel X38 * CORSAIR 2GB (2 x 2GB) XMS2 PC2-8500 DDR2 * XigmaTek HDT-S1283 * BFG GeForce GTS 250 OC 1GB * WESTERN DIGITAL 500GB * WESTERN DIGITAL 250GB * ANTECH Nine Hundred Case * PC Power & Cooling S75QB 750W 80 PLUS Certified Active PFC Power Supply * SAMSUNG SyncMaster™ 931BF LCD Monitor * Saitek X52 * FSX Setup FS-GS *

and with this I don't see any FPS hit at all in FSX with the 727 or the C-130. In fact, they don't cause anymore FPS hit the the default FSX 737.