If it's TT competition you crave, cars in TTF-TTB can always bump up to a faster class. I've seen it many times when there is competition in a faster class. The bumping car in such an instance can run with less weight or bigger tires (among other allowances) to make up for the bumping to a faster class. For example, a TTC car that has 100lbs of ballast can shed the weight if they bump to TTB. There are TTB drivers register for Thunderbolt, so bumping might make the weekend TT competition more interesting. If the bumping car makes physical change from their TTC trim to TTB trim, the bumping need only to provide a revised classification form for the car. If we can get more TTC guys to run, that would be ideal.
For more information on TT competition, classifications, results, season points and track records check out: http://www.nasa-tt.com//Northeast