OK, I just tried the T-38 out on my old rig, and I flew it around solo with the FPS locked at 29, and it stayed steady in normal sized city areas. Again, my old rig has a QX9650 CPU (OC'd 3.8 GhZ), a GTX 8800 vid card, 4 GB of DDR2 memory, Vista 32 bit, and a 30 inch monitor at 2560x1600 resolution. Sliders varied, but the important ones were the scenery complexity (3/4) and autogen (1/3)....keep in mind the 30 inch screen uses alot of resources. Your results may be better.
I have the Aerosoft F-16 and used it as a comparison to the T-38 in a couple of areas flying solo, and then with a wingman. The F-16 is much, much heavier on frames than the T-38...probably because of the HUD and glass displays in the F-16. So wherever you fly the F-16, expect to get better and steadier frames with the T-38. With a T-38 two ship formation, expect to get about a 40 percent frame improvement over that of an F-16 two ship formation.