I plan to use my cyclocross bike for road cycling. In particular, I'll start in a triathlon, where I'll need to do 45km on the bike. I would like to maintain the speed of 30km/h throughout the race. The bike is equipped now with 700x32c tires (specialized borough cx). Many people say that I should change them to some 25mm. However, I've read on this forum that narrower tires have greater rolling resistance.

What tire would you recommend in my case? Note that I don't plan to go much faster, I'd rather like to keep 30km/h for the whole 45km and be as "fresh" after the ride as possible.