The finding of 37mm marathon's being lowest rolling resistance is an interesting one. However I wonder whether the relatively good performance of the marathon line is a bit of a fluke. The greenguard and also the thicker smart guard is partly latex which has lower impedance than butyl or straight up tire casing. Even the people at BRR suspected that said (partly) latex belt worked in some effect to reduce rolling resistance as it's a piece of flexible material between the tread and the inner casing. It could work as a tiny piece of suspension that showed up in drum tests.

How that strip shows up for a rider however, is a different story. I use marathons, marathon plusses and marathon winter plusses when needs call for them. But in my mind marathons at least are slower than the test numbers would indicate. I'm fairly sure the winter hasn't been tested and I'm not sure about the marathon plus. The super stiff sidewall doesn't flex much at all which means that the rider experiences a lot more chatter and bumps than one would with a suppler tire.

The mondial is a super slow tire on a drum test, but it does have pretty flexible sidewalls. It's in my mind not really a slow tire either.