I am running the ZZR1200 drive and with a new 120/70 Michelin Pilot Power it is about 1.5-2 mph slow at 100 mph and on the money after a 1000-1300 miles or so. When wore to a nub it's still within 1 mph at 70. Roadsmart and Avon are both different with the Avon reading slower than the Michelin and the Dunlop reading noticeably faster. I do not think there is that much rollout difference, but the speedo says something's up. Just my .02
EDIT TO ADD:
I changed my gauges after my 09 crash and had a huge change in readings though I had the same rim and speedo drive... like a 5-7 mph difference at IIRC 100mph (I like to check it at 100 because the faster you go, the more accurate your GPS is and at 100 mph the percentage is a cinch to figure). So gauges are not all created equal for sure.