From my conversation with the Ford rep at the 40th anniv celebration at Nashville, the new transmission performs much better than the current one and is close to the 5 speed in seat of the pants accelleration. However, it may not be as durable and has a lower torque rating than current 4 speed. There was a post from a Ford Mechanic on this or another site who works on transmissions and he said this is has a lot of problems in the Explorers and is totally electronically controlled. He said that Ford has issued numerous recalibrations to band-aid the problems. The design is apparently close to the trans used in the older 4-cyl Mustangs with an extra gear. Of course, Ford may or may not have fixed these problems, but if the past is any indication of the present, I doubt they have all the bugs worked out.
Reduced durability and other issues really concern me, and may delay my purchase of the car until the trans has a proven track record in the Mustang. I don't want a manual trans for daily use. I also want to be able to add a power adder to the car and not break the trans.