If the OEM tires are good for 4-5 events, I would stick to the OEM tires as the MRC calibration is based on that specific compound and width. If not, I would suggest you to take a look at the 19" wheels as there are a lot more options on that size since it's more common.
Other advantages of the 19" setup;
weight reduction
cost
shorter gear ratios
longevity (NT01s are arguably the longest lasting tires for track use)
You may also want to check out my related thread:
http://www.camaro6.com/forums/showthread.php?t=493514