And if a road bike really doesn't feel right, you can get a "fast hybrid" that will be comfy, too, if you put skinnier tires on it. I put a couple thousand miles on my hybrids each year, and the "slower" one is a little more comfortable over the long, long haul (so I took it on the week-long tour); the fast one is great for one-day centuries (7500FX Trek).
WHo knows, you may be able to tweak the comfort bike so that at least it's comfortable over the longer distances. Then, indeed, when you get a lighter steed it will FLY because of the strength and endurance you've built up - and in the meantime, as you get stronger, you will get to make some of thsoe folks on the really lightweight stallions who don't pu tin your mileage feel a little sheepish...