The NS3s will handle the mids like a champ with it's long excursion, but overall volume won't be too high and I had problems getting the top end "sparkle" out of them I wanted running full range (and I don't like "bright" highs). As mids they were exceptional though. The Whispers could be a better option, but I just don't think they'll handle a 500hz HP. They sound great, but aren't very robust or forgiving of extra power. I can't speak for the Fostex, but I'd love to try them sometime.
OP: try the TBs and see if you like them. I've tried a few of their drivers, and use them currently (w5-704d) in my setup. Remember that high excursion drivers with a lower FS will give up sensitivity in almost all cases, but also consider that the closer your crossover is to the FS the more harmonic distortion you'l encounter around the crossover point, and phase integration can be a problem as well due to the impedance spike at FS (which can make the speaker "stand out" too much instead of blending into the midbass). Ideally something with an FS around 150hz and 1-2mm of linear travel would be ideal, but I think you can get away with the limited excursion of the TBs from mounting them on the dash, where you'll get a natural boost in SPL from the waveguide-like effect of the windshield and side windows. Be forewarned that mounting them up there might create a few peaks and valleys in the response though, so a good EQ might come in handy.