I'm probably one of the few that has owned, driven and lived with both an E92 M3 and a 2004 SVT Mustang Cobra, which with the right add ons, (subframe connectors, strut tower brace etc) was very close to the M3 in performance and not much inferior in handling, but at that point the similarities end. That group of SVT's had independent rear suspension so were much closer to the M's than the current G500's.
There is or would be no question as to which car you'd take a 1000 mile drive in, and for those that keep referring to track times that's the real difference. Which car can you live with and as long as you're comparing the Boss or G500 there isn't that much difference in price.
Keep the silly emotion out of it and ask yourself . . . "which car would I rather live with?"
Besides the new Mustangs are so darn big.