A) Have you actually seen this, or are you just speculating? I, personally seriously doubt these claims (with equal drivers). Granted, the smoother the track, the less the
suspension matters, but who races on glass?
B) That isn't exactly a stock v. stock comparisson. What about when you upgrade the Vette's springs and shocks just like the Mustangs--you still think the 3-link Mustang will win?
C) If the solid axle is good, why is it Ford decided to force a poorly designed IRS system to work on a solid axle chassis in the first place?
D) Have you, in recent memory, heard of any solid axle car beating an IRS car in a road race competition?
E) Not many people will be taking these to the track, so the advantages of IRS on daily driven roads becomes huge.
The simple fact is, IMHO, the $300 in parts that Ford reportedly saves for the IRS would have been a HUGE benefit for the Mustang. It not for the image alone. Sure, keep the solid axle--but as an option. I really hope they offer the IRS in a sub-Cobra level Mustang -- say GT350 with a slight hp increase for, around $1.5k more.
Otherwise, I will also have to consider other options. GTO perhaps? Of course the Mustang will be in the running -- and when it comes out I will see how much difference the IRS makes. Who knows, I may be surprised at how well Ford has pulled off the solid rear axle and it won't be an issue.