You ride essentially the same size road bike as I do. I have three different mtb's - a 16" Scott (probably a little too small), a "medium", between 18 & 19" Klein Pulse II (about right to slightly big) and a converted 21" (55-56cm) 1987 Trek Antelope with Forte Gotham street tires. Pressure is maxed at 75 psi and I don't know that I'd want to go any higher. Those tires are pretty dicey on gravel but great on the pavement. The Trek rides great and is my "slow" bike based on the way it's geared.

It does have a longer top tube - approximately 23" (58cm or so). It wasn't so much of an issue with the original mtb bars because they were swept back a little. With drop bars I had to use the original stem which had very little forward reach and move the saddle forward just a little bit. Overall, it's a decent ride from a comfort level but not one where I'm going to be riding stretched all the way on the hoods for long periods of time.