I have no idea on the gear ratios for 80. If I had the $$ and was willing to really cut up the floor, I would look at the TCI 6spd auto. But I am a poor white guy with big dreams!! :D So that leaves me with the 200r4. I think that with the GNX's running around with trans in it should say something about the strength of it. I think getting the right tranny guy is the ticket. These are fairly light cars(Mopar Abodies) so I think with the right build, it should be fine. But I am no expert! I can understand your concern about the strength with your hp level. I will be lucky if I seen even 500hp so I am not worried. This is a tough call!
Remember anything can break...few things are truly bullet proof!