The RBT 6 is going to give you a 3.2something first gear. 6th would be about the same as the 5 speed.
So what it is more or less doing, is making the car pull as if it has the 5.00 ring and pinion in the car instead of the 4.22.
Essentially it would make a Pantera with a "built" enigine pull like Halls "Root Beer" GTS car, which Mike Cook drove into the 9 second 1/4 mile times, front wheels off the ground and all at launch.
Who knows what you will break with that type of launch capabilities and where the body will crack, but I'm sure it will somewhere, big time?
If you look at the original ratios in the Pantera, the 2.20/4.22 makes the car pull in first gear like a Mustang with a Ford T&L and a 3.89 rear would but gives you the top gear cruising of a 3.00:1 rear,and true close ratio gears in between.
Even today that's pretty sophisticated.
People who complain would be better off with driving an automatic transmission in a non performance vehicle.
Noticing what most Pantera owners are looking for is top end cruising. When I called RBT about rear ratios (looking for the 5.38) he presumed I wanted to go lower then the 4.22, not higher?
For about 98% of Pantera owners, the existing 5 speed is fine, even for track or racing use.
Only two applications I can think of that would justify even the RBT 6 speed, maybe, would be running at the 24 hours of Lemans or Daytonna at over 200 mph or drag racing in some sort of vintage match racing?
The RBT 6 speed isn't a perfect animal either. The three extra inches on it put it into the a/c condenser in the rear of the car and the shifting are somewhat of a unknown as well with the strange Pantera rod shifter mechanism?
I decided long ago that for me the stock 5 speed is much more than adequate. Perfection doesn't exist. The wheel is already round.
I even put Webers on the car to kill some of the power the 351 is capable of so it won't hurt the ZF?