[California]

Yes, it sure seems that way, thats my intention, when I decide which one I'm going to get.
PS Engineering makes a great 17", original styled rim, that with some Michelin Pilots.
With your Superformance, you could go 275's in the front(with no rubbing), and 335's in the rear. Tires and rims is about 3K to 4K, depending upon the finish of the rims. What an awesome combination. Great looks and tremendous handling, you could really put the power to the ground! Thats the big issue with the 15" set, to easy to break loose.
Some people have an issue of the look of the 17" rims, that it takes away from the originality, but that shouldn't play any role, since 99% of the people here do not own an original 65-67 Shelby Cobra anyways. Thats my perception at least. My view is if you want performance, and want to rest a little easier, when your speeding down the road, go with the upgrade.
It really is a pity that none of the big 5 tire makers, don't seem to put out a wider z rated tire!!!!
Nick