My choice in rear gear+ overdrive puts me slightly below stock RPM w/ the 200-4r and gives lots of torque on the bottom for my little I6 (3.23 to 4.11 +OD). Add the oversized rear tire and it puts me about on par w/ a 2.80 rear gear. I think you lose a little more efficiency with the OD vs. a tall rear gear though, but the trade off is worth it for me.

For extremely high torque applications i've heard that the 4L80E or a GearVendors is the way to go, as both the 200 and 700 are weak for low end torque in big #s.

GM dropped the 4L60E (700r4) in favor of the 4L80E (th400 w/ OD) in their HD truck applications because of problems. The 4L80E is computer controlled, so you would need an ECU or a manual shift version... big $$.

http://www.chevellestuff.com/generic/rpm_calculator.htm
says you should be running ~3100rpm@80mph depending on tire size and converter slippage.

If I ever build a street rod, it will probably have a GearVendors in it.