You 5.0 guys are really lucky to have an auto with potential. As I understand it, the 6R80 is based on the C6 which is mega beefy. Although there isn't alot of performance parts specifically out for the 6R80W (yet), if it is based on the C6, Development of these components shouldn't be too difficult.
The pre-05 stangs is based on the C4, and can be made to handle pretty amazing torque.
The 5r55s in the 05-10 stangs is based on something else totally, and is a total piece of junk, which is on borrowed time above 500 hp. There hasn't been a whole lot of success in being able to beef it up either.
So is the guide to on how to decipher the trans designation
The first number is for the number of gears
The second letter is for rear or front wheel drive
The next two numbers indicate the torque capability in NM divided by 10
I can't remember what the last letter stands for.
By the codes:
A 4R70W is a 4 speed, rear wheel drive with 700 NM (or 516 ft-b) capacity
A 5R55S is a 5 speed, rear wheel drive, with 550 NM (or 405.7 ft-b) capacity
A 6R80W is a 6 speed, rear wheel drive, with 800 NM (or 590 ft-lb) capacity.
So you 2011 5.0 guys have a very promising auto trans. I will probably swap my 5R55s out with a 4R70W just due to the fact that there are conversion kits out for this swap. But I would like to see someone swap out a 6R80 into a 05-10 stang.