I have ridden MoM five times-- once the century, and every time since has been the double metric. The last hill is brutal (applies to both rides)-- but it is not the steepest, nor the longest. It is a matter of placement-- your legs are beat by the time you get to it, and it is a tough climb.
I would definitely encourage you to sign up for the double metric. You do 4 major climbs (as opposed to 2 on the century). That includes the longest climb of the day (first major climb--straight out of a rest stop) and the most rural, which is a beauty--and very steep. Since roughly 10% of the field does the double metric, you don't have to deal with crowds (except the first 20 miles or so where the routes are the same). THey send you off in groups of about 100 spaced a few minutes apart, so there is no real issue with crowding.