OK, heres the basic order of performance auto trans in mustangs, it goes AOD-E , C4 , powerglide/400 . the aod-e can be made to handle power but they're not as reliable in my opinion as a c4 and they take more power to run, the c4 will handle anything up to the 8's with the right parts but at that level they require checks and freshen ups, the glide and 400 are both top dogs that can handle whatever you got.
In your case you're really fighting 2 battles, if you go c4 you will most likely be happier with a gear change to 3.55-3.73 so you have to factor that possibility in, if you keep the aode then you can keep your gears and you shouldn't run out of gear unless your shift points are a bit low but you should be around 5800 rpm shifts. If you want to keep the aode then a rebuild with a shift kit by a local trans shop would be the equivalent of taking it to the top of a building and tossing it of the side and the same goes for any trans you want to race with. So , whatever you go with be sure its gonna be built right by someone who knows these cars and what the intended use and power its gotta handle.