I've ridden all six CNCs, and always on a road bike, but don't see any significant--meaningful--advantage for road over hybred other than use of energy differences. (The exception would be a road bike with inadequate low gears for the mountains but that should be less of a problem than usual on this years ride.) The road bike will probably have slightly less rolling resistance than a hybred and the hybred will have less than a mountain bike but I've seen people on CNC using what appeared to be a 50 pound cruiser with gears. I'm also convinced, by observation, that recumbents aren't as easy to push up the hills but a number of people obviously feel that the added comfort is worth far more than any problem of slower climbing. (When my butt begins to hurt on the 5th or 6th day, I can identify with their assesment.)  It is clearly an individual choice with some gains, or lossess, that you will need to determine for yourself but either will work fine if the engine is properly tuned. (-:

I say ride the one you will be most comfortable in after 450+ miles.

If you decide to ride the mongoose, spend $20 and get some slick tires for it.  That will make a noticeable difference with your speed (rolling resistance)