AlbertaBeef, I agree with most of the above, but there are some other reasons. My '89 Cannondale became 'slower' when I replaced my integrated shifters to DT shifters, my 2X8 bike is faster than my 2X5 bike because of the better selection of gears. Overall weight takes it's toll over many climbs and heavy tires and wheels hurt acceleration, but may actually help on relatively flat distance rides.

I've been riding my Cannondale touring bike on my unloaded distance rides in spite of the fact that any of my roadies could cover the distance more quickly. Take whichever bike you feel is more suited to the mountain century, have fun and don't worry about the speed.

Brad