The reduction in rolling resistance comes from two sources: a high thread count per inch tire carcass and high inflation pressures. The former is neutral to positive for comfort, the latter is detrimental to comfort but under your control. Continental Gatorskins and Grand Prix 4 Season tires as well as Vittoria Randonneur Hyper and Pro tires can be had in widths of 28 mm or higher, with high tpi carcasses, and can be inflated to reasonably high pressures. Some of their road tire models may offer a 28 mm width too. Other brands may have similar models if you check, those are the two I am most familiar with except for Hutchinson who don't seem to believe that people who want wide tires also want efficient tires, unfortunately. There is a third component to rolling resistance, namely width. However, contrary to common belief wide tires have less rolling resistance than narrow tires when width alone is varied. The most efficient tires are developed for road racing though and at road racing speed the aerodynamic performance is critical too. So tire makers tend to make their road racing tires with the most efficient casings and pressures but in narrow widths. Wider tires are seen as less sensitive to efficiency in the consumer's minds so they tend to get second, third, fourth, ... rate materials and construction techniques in the mistaken belief that we aren't interested in high efficiency tires. Actually at the speeds many of us cruise at the tire rolling resistance is a higher penalty for us than it is for the super fit, Mach one, road racer. Other things contribute to tire casing efficiency of course and some of the very desirable ones like puncture resistance can have a detrimental effect on efficiency.

So, you can find some quite excellent (though probably not quite best in the world class) 28 mm tires. Tires of that width offer a reasonable level of performance on surfaces that hybrid riders expect to tackle and road riders avoid if at all possible. A high pressure wide tire can be run at lower pressures for comfort when conditions demand without becoming an invitation to pinch flats and 28 mm is wide enough to offer some of the wide tire comfort advantage. Even wider tires are available with fairly efficient construction these days but 28 mm is about the widest width that is offered with near elite road tire performance by the three brands I have studied the most. I am planning to try a century this year and I am currently thinking I will go with 28's for that event. My speed won't be high enough to benefit aerodynamically from narrower tires and the best 28's will roll as well as all but the very, very best 25's and 23's. Whatever difference there is may win a race, it is unlikely to prevent me from completing the event or make me noticeably less tired at the end.

Time to start training in earnest though....

Ken