The ecoboost V6 makes 350lb-ft of torque from down low, so I dont know that you could tell a difference between the engines based on the power-band. The only difference would be the sound. I can see them putting an ecoboost V6 in the GT, and an ecoboost V8 in the GT500. Those of us who need V8s would have to step up to the GT500. (or buy used older GTs)
Who knows, I think this happened before with the fox bodies in the eighties. They offered a turbo four as the performance engine for awhile, (the LX?), but everyone kept buying the V8.
I think Ford would be better off finding ways to make V8s more fuel efficient, like cutting them off while stopped, or deactivating cylinders, or even a hybrid electric drivetrain for use in the city.
Believe it or not, there is more to consider than just simple mathematical equations like power to weight ratios when buying a PERformance car. That is why people like Jeremy Clarkson have jobs. You want a car that is going to be exhilerating to drive. A big part of that is the power to weight, but you also have to consider drivetrain, durability, comfort, styling, handling, heritage, sound, soul, character. These are not things you can put into an equation, and the Mustang has them in droves. If numbers were the only thing to consider, we would all be driving Mitsubishi EVOs. Nothing against the EVO, it is a great car, but I think 180 degrees different than the Mustang. So, Katrina, may I suggest you go date an EVO driver, and then you can enjoy the pleasure of pure, mathematical PRE-formance.
The ecoboost is a great engine, just not sure its right for the Mustang. Maybe ford should bring back the probe and put the ecoboost in that.