I don't think the Supra or Corvette compete with the Stinger much at all. If I had wanted a 2-door, 2-seater, I would not have bought a Stinger. This replaces my '05 Legacy GT wagon, because that died, and I have a spouse + 2 tweener kids that will need to ride with us for another 6-8 years minimum, and for ~$40K, there's nothing else out there that competes with the same power level.
The Q50 isn't going to be doing much (desperately needs a radio upgrade, and maybe a better transmission, but Nissan has issues), the Chevy SS (sedan) is getting harder and harder to find and it's used only.. About the only viable competitor to the Stinger out there is the Charger SRT - and it doesn't come in AWD, and I don't feel like spinning tires all the time.. Test-drove a Scat pack, and I chirped the tires while GINGERLY turning a corner.
I took me 3+ years to decide on a new car - my wife would kill me if I got rid of this one now..