Hate to sound like the negative nellie, but about 14mph was as good as it got for me on my hybrid. I used it to get back in shape from my flabby 260 to my now fairly low bodyfat (15%) 218. After that not only was I slow, but once I could actually do more than 10 miles at a time my body just hurt constantly from knees to butt. I blame it solely on the suspension.

I never thought I'd be able to ride a roadbike, but I gave it a shot and ended up buying a full carbon fiber trek pilot. The CF gave me tremendous shock absorption with NO discomfort whatsoever, and I can now hit 18.5-20mph on the flats without a problem, and I'm getting faster.

YMMV, of course, but even now I would find going back to the hybrid I had impossible for a century. I can do 40 miles in two hours with no problem on the road bike, and have no concerns about doing a century. On the hybrid I would be in agony after 15.