The question comes back to what are you doing (or going to do) with your Cobra? A track day or two, Auto-x, or just a better (Sticky) street tire? A track day, Auto-X tire (whether 15-17-or 18) will not be a good street tire, and vice versa. Treadwear on those (track, Auto-X) tires are 100 or less, you may get 1000-2000miles out of them on the street (and even worse traction if temps are under 50degrees, those kind of tires like lots of HEAT!). Also remember these are High HP, lightweight Cobras, you will overpower "any tire" with just a little push on the "right" pedal
I see a lot of money spent without much gain. My Experience: 50years under my belt, Auo-Xing, Track days, Road Racing, in this madness we call Sport Cars, Shelby always left off the s in Sports
My $.03, Cheers TommyRot.