Have those who use MTB frames used a larger sized frame than you would for a dedicated mountain bike? I have a Trek 750 hybrid frame I may use, since I can't seem to find a reasonably priced used frame in my size. I would ride about a 60 cm (c-c) traditional road frame, but this Trek 750 is only about 53.5 cm (c-c), though it does have a slight slope (about a 1" rise from seatpost to headtube.)
I have found an adjustable stem that will allow me to raise the bars to a comfortable position. But for the purposes of keeping with the theme of this thread, and to repeat a question lev has already posed, is there a great loss of efficiency with a smaller frame like this? I've read there is, but not seen much in the way of explanation.