I rode my cyclocross Kona Jake 60 miles a couple of weeks ago. The only thing uncomfortable was the pressure on my rear end. I can't imagine a more upright bike would have made that better. I also noticed that most of the 1600 or so other people on this 60 mile ride with me were riding road bikes.

I should add the caveat that I did a lot of ab/back exercise training for this ride, but, hey, if the goal is to get in shape....

But I don't want to discourage you if you want something with flat bars. I've got one of those too, and it's nice. (I would add, though, that cyclocross bikes are reasonably "heads up.") If I were riding 60 miles, I wouldn't worry too much about speed, but I think there are a few things to look at in how fast a bike will be. (1) How heavy is the bike? Lighter bikes are faster, but much more expensive. (2) What's the gear range on it. Check out this link (http://sheldonbrown.com/gears/) for a handy online gear calculator that will tell you how fast a bike will go at a given cadence. (3) What kind of tires are on it? But faster tires aren't as comfy, so for a 60 mile ride you might want to ignore this factor.