Seriously, I am on a Z kick with mine right now. I have riden R's, including put a lot of time on my brothers 83 air R. The 250r has a smooth power band that pulls all the way through. It is a very well engineered and well built bike. On the other hand, we have the underdog, the Yamaha Tri-Z. The Z was not dominent in the racing days of the 80's. The Tri-z has a light-switch power band that will put fear in you. It was not traditionaly raced because it will wear you out on the track with the weight distribution, and speradic powerband. There is currently 300 kit you can get for it, including an assortment of other aftermarket goodies to help a Z put a whoopin on most anything that pulls up next to you.
If I were to build a drag bike, I would follow in Yamahondaman's footsteps in building up a Z.