The standard height GSO Crayford has less by about 1/2 inch iirc. You might find that some Televue EPs no longer reach focus without a barrel extension.
David - I bought one for my 8", which is what I'm guessing you're considering. I have to have a 35mm extension tube inserted to get achieve the same out-focus as I had with the original R&P.
Am I happy with the difference in smoothness, stability and adjustability? You bet. Makes the whole scope feel much nicer.
Are you coming to the public night at the University domes tomorrow evening?