Pacer
I have a Surly Pacer among other bikes. My commute is about the same distance. The Pacer is a nice bike for this purpose. I had a Surly Nice Rack mounted on the back with some Chrome Industries bags. Fast commute and packed all that I needed, plus.
I picked up a Surly Crosscheck thinking it would be a better commuter bike but the frame felt really sluggish compared to the Pacer. Sold the Crosscheck. I am with you on a steel frame road geometry bike, able to accept a rack, being an ideal commuter for that distance - 30 miles per day.
That Midnight Special 650b looks really sweet.
Lots of great choices out there.