Zr1 = Supercar, but why can't the Shelby GT500 with 500 horse come within 6 lengths of a C6 Z06 with 500 horse let alone a Zr1. It's sad for $50k GT500's only run low 12's at best with 500 horse, hell I run high 12's with 330 flywheel horse power.
Weight and suspension, pretty much seals the deal for Z06 and ZR1.
GT500 is an awesome car but is overweight and the suspension setup is nothing short of prehistoric. To even come close to competing, SVT will have to make MASSIVE changes, which won't happen.
I don't think competing with the Vette's is a priority of theirs though. They just want to make a good mustang, which they have accomplished.