Let’s be specific here about the S550 Mustang power ratings:

3.7 liter V6 – 300 HP and 280 TQ (a bit downgraded)

2.3 liter 4-cyl turbo EcoBoost – 310 HP and 320 TQ (all new, all good)

5.0 liter “Coyote V8” – 435 HP and 400 TQ (a bit upgraded)

And here’s the full price list.

Official 2015 Mustang curb weight info.