One of the development cars was shot with Pirelli P-Zero P245/45-R20s on the front. The rears LOOK bigger in this pic, but I can't say for sure.
http://jalopnik.com/photogallery/200...Ext/1000407529
These are the 5-spoke concept styled wheels.
It looks like the cars on the top of the trailer are using smaller generic wheels. I'm guessing V6s, and they didn't have prototype wheels ready in time for testing these cars.
The way GM has been going with their dealer accessory programs lately, I'd fully expect there to be a long list of stuff you can tack on when you buy the car. It's well engineered stuff, it doesn't void your warranty, and you can tack it on as part of your financing.
I just wish they could find a way to offer their remote start system on manual transmission cars :(