I believe the NT01 and the RA1 are the same compound, just a different tread pattern and branding. Toyo and Nitto are brands within the same company. I always considered all the rubber before the last mm to just be there to allow a drover to break them in until they get the most grippy in the session before they show cords.
One knows one is over driving one's tires when one hear the crunch of sheet metal.
