<----That is a 2006 Kona Smoke. Though marketed as a hybrid/urban bike (part of their asphalt line up), it is essentially a rigid mtb with 26x1.5 slick(ish) tires and 42/34/24 triple and 11-32 cassette. Back when I had a commute, avg speed was 14 mph, cruising speed was 17 mph, and my "I shouldn't have hit the snooze that third time..." was on the high side of 21 mph. It also has 16.3" chain stays, so heel strike has been an issue.

In other words, it can be done on a 26" mtb.