My two main commuters run 700:28 Marathons and 26 by 2 Schwalbe Hurricane Sport tyres (559:50) and although there is a definite difference in rolling resistance the 26 by 2 tyres (at 75 psi) still roll out very quickly and I can maintain very good speeds.

The 26 inch tyres eat up the bad roads with wanton abandon and I roll over and through things I would be dodging with the 700:28's which run at 90 psi.

At the end of the day, (or the commute) there is not a lot of difference in travel time... and the bike running the 26 by 2 inch tyres is also a fixed gear.

I also have several fixed gear touring bikes that run 26 by 1 1/8 tyres (vintage Dunlops) and 26 by 1.5 Marathon tyres and have been clocked on the 26 inch Marathons at 37 kmh (cruising) and have been able to maintain a speed of nearly 40 kmh on the vintage bike for an hour straight.

I was simply amazed that a smaller diameter, higher volume tyre could roll out so fast, especially when their max pressure was 60 psi.

Of course... when I want to go faster I saddle up the vintage racing bike that runs on high psi tyres that are 630:20.