Typically they say you can run a 26" tall tire if your making at least 400awhp. Not sure I'd want that tall of tire at that power level but anywhere from 550-600+ & you should be alright.

When do you need to switch into 5th gear, above 150 mph? I would think the 24.5" tall tire would be the quicker tire, as long as it didn't require an extra shift vs the 26" tall. Though I know alot of guys that are in the 550-650hp range run the QTP's @ 26" tall, instead of a 24.5" tall tire, not 100% sure why they went that route.