This has been pretty odd, but for distance I do the same times on a road bike that I do a MTB. BUT....I am faster on sprints on a MTB than i am a roadbike. I ride almost identical gears on both...it's kinda weird. Could this be a fit issue, or do i have to develop form for the roadbike, etc?
for what it's worth, I've been riding roadbikes for only a couple months, but have rode MTBS since the begging of the year, and have put over 10x the miles on MTBs than I have roadies...so could it just be having to get used to roadbikes?