Just to jump back to the thread. Another thing with tubs is that the profile is much rounder than a clincher, making it generally feel better for cornering fast. However, the increase in pressure isn't always helpful except on really smooth roads... I've gone up from 18mm tyres to 23mm and have noticed a vast improvement in comfort... and a very minor improvement in speed on typical british roads. 18mm were run at 130psi and 23mm at 100psi. I know there are two factors there, but stil....
For the cost of 3 replacement tubs you can buy a set of clincher wheels :-)
djb