Mondo, something else to keep in mind is where you are. I can do rides here in the Dallas area that have 8,000' of elevation gain. Well, that turns out to be a 160 hills 50' high or something. Meanwhile, in your area, a ride with 8,000' of elevation gain is liable to go up two or three long unending grades. I think a few long grades are probably harder than a bunch of little hills, given the same total climb. Then also, if you start in Denver and climb 4,000', you're getting into a little thinner air which adds to the difficulty.

It is not uncommon to see numbers considerably different for the elevation gain of a course, so take any of those numbers with a grain of salt. Those numbers probably vary more on the bunch-of-little-hills courses.

What is "steep"? Generally, the freeway passes there around Denver don't exceed 7% grade or so. The more rural and less-well-built a road is, the steeper it is likely to be in that area. But a hill of any length that is 7% is going to slow me way down on a bike, and will get me rolling fast in a hurry on a downhill.