I ride an Mtb with 2,1 tires, a CX bike with 1,4 and several roadbikes with 23 or 25 mm racing tires. My commute is only 4 miles but the difference in speed is significant. My advice is (stingy retrogrouch): Get a good quality japanese roadbike from the eighties on CL. My 87 Team Miyata is as fast as my CF bike and in some respects a nicer ride.