you're riding really hard, and understandably running thru tires quickly, so you've got the chance to experiment. slip on a set of Pirelli Diablo Rosso Corsas. I don't think you'll find much different grip than the T20s, and my experience has been that they last a bit longer than Bridgestones. and they'll carry the bike right down to dragging the peg feelers on the track... I think generally Pirellis are amongst the most expensive tires on offer, but there's a reason for that!