I guess the jury's still out on official weight. Here's a C6 thread with some 'spirited' discussions and even an MRR contact who chimed in on pg 4. Sounds like there were -some- balance issues 7 years ago.
OP, I can't answer your "+" size question but I have loved these wheels so far. Had two sets of rear tires on them. And I WAS a big fan of Pirelli's, color me a Nitto fan now!
https://www.camaro6.com/forums/showt...=477000&page=5