Early preproduction GT's didn't even have the production cars S/C 5.4, they had the '03 Cobras S/C 4.6. Also, the increase in performance, all around, is a product of tuning the engine and chassis to final production specs.
The car used in the lates MT article was a preproduction pilot car. If you don't follow automotive manufacture, let me enlighten you. A preproduction pilot car is a production spec car. They are called pilot cars because they are used to check the manufacturing processes in the plant. These cars are rung through the ringer to check that all of the production spec pieces are working as they are supposed to. These cars also allow the line to "fine tune" itself for fit and finish........... and to see if there are any manufacturing difficulties that need to be ironed out.
The ramp up of the manufacturing of the Ford GT is very slow. There are many processes being used that Ford has never used before (nor anyone else as proofed by all of the patents that Ford has gotten on them). Also, I would imagine that the parts suppliers are being rather slow also, as Ford is being extremely picky with these cars.
BTW, according to a person who worked on the electronics for the car......... the stellar performance of the pilot car is due to the tuning of the electronics. This has been a work in progress, with these latest test cars being the first of those tested with the production tune. Boost was not turned up on the engine at all, over the course of preproduction.
I think the thing that people here are not looking at is that this car has been completely developed in the public eye. Journalists have had access to the car at all stages of development. They have tested the car at all points of development also. Also, this car has had a very short development period. From concept to production was only 18 months. Thus, the slow ramp up makes even more sense.
Just as a FYI for those who have a SRT-10.......... according to all tests of production spec cars, the ride and daily driveability of these cars is amazing. As my latest R&T stated "But it's also a car that is comfortable to get into and out of, that has very good ride control, excellent seats for two and all the amenities you could wish for. As Ellida and I sailed up Pacific Coast Highway, we both grinned and agreed that this was one supercar in which you could easily drive for hours on end without turning into a pretzel."
Mind you, I'm not saying it is "better" than the Viper........ as better can be a pretty subjective word. Just that it is a pretty amazing car that does deserve respect, even if you would never buy one.