I've owned four SVT prepped Mustangs over the years, the best for road work was the 2003 when they opted for an IRS. The problems with it showed up the first day I owned it (along with 5,000+ other owners who all complained loudly) in that with it's immediate power the engine over-ran the axle's ability to launch the car, which manifested in the form of severe (and I mean severe) wheel hop. I bet Ford replaced 100 IRS systems in the first month! Everyone wants a road course worthy sports car, the problem with that is simple - it will not win drag races. My current SVT/Shelby Mustang dyno's over 600 rear wheel HP - If it had IRS it would break the first time you tried launching that kind of power. Hell, it hops like a rabbit now; the live axle takes a real beating, but it's made to take that beating.
I've also owned Corvettes and enjoyed the experience, but I had my butt handed to me in too many straight line races to stay in one. Just can't hot rod them like you can my current ride.
Just my 2 cents worth. Both great cars, just not designed from the ground up to be real competitors, even though Shelby touts his product's road course worthiness which even comes out in the attached article. It can hold its own, just not against a world-class car such as the Corvette.