Eh, it might be tires, but I think Ford just wants gearheads to get the V8. Speed ratings on tires have to do with sustained speeds - that is, H rated (130) means the tire is rated for a
continuous 130, such as between Austin and Dallas. S rated tires should be fine to a quick burst to 130ish. It may have to do with other driveline components... or more likely,
wussyfied kill-joy lawyers. Or, that an ungoverned 300hp Mustang - even if it is a V6? - would have GT-like insurance rates.
Either way... a shame to see a three hundred horsepower six-speed Mustang governed, so that a Honda Accord can outrun it...
I know that you can get a package that includes 255/40R19 Pirelli P Zeros with the V6, but the limiter still kills the fun at 114. I suspect that a 3.7 Mustang, w/o limiter, would be good to around 140something.
I had H-rated tires on my '88 LX5.0, and they were fine for the occasional poke up to 130+.