[427sharpe]

Stick with a well built C4. The C6 is a heavier duty trans, but it also loses more power to parasitic loss than a C4. Most trans builders offer a reasonable C4 that will live very well behind the engine you describe. Almost any reputable builder has fixed the inherent C4 weaknesses (bands and clutch packs). Art Carr comes to mind immediately. The FMX would be my absolute last choice for a performance trans. I would be wary of any off the shelf AOD as well, because they were known to lose the OD (burned governor) if the plastic linkage clip fell out of adjustment.
If you want to go with an AOD for the overdrive, get one from a good performance builder. It will have all the HD goodies, as well as a shift kit to bring the rpm shift ranges up, and make the shifts crisper, with less slippage which will give a lot more life behind a performnce motor (or in a perfromance car). Makes the car a lot more fun to drive as well!