Originally Posted by Daily Commute
Old Fart has some good ideas. Also try bike pants with better padding. I think a folding bike would be too slow for those distances. A more upright "comfort" bike would be slower, but less slower than if you had to give up cycling to work because it's too uncomfortable.
Also, if you have the bucks to drop on another bike, look at cyclocross and touring bikes. They have dropped handlebars you can use when you want to go fast, but they also have a more upright geometry.
I commute on a cyclocross bike, and love it. A touring bike would be even better though I think for distance commuting. Check out different seats though, That might do the trick. Also, at least consider some sort of bike short if you dont already use some. Many people find them more comfortable since they have a layer of integrated padding and better sweat wicking properties. (Ignore the bikeshort threads on this forum as being more or less moronic
- go with what works for YOU!!) My gut feeling is that you will tire yourself out too much on a heavier bike. Good luck