The narrowest Marathon Efficiency is 40mm so it's not a direct replacement for the discontinued Supremes. 40mm is wider than I need for the type of touring that I do, so unfortunately this tire is out for me.
In any case, looking at the Bicyclerollingresistance.com ranking chart, the Continental Contact Urban is a better tire overall than the Efficiency, with similar rolling resistance and weight but significantly better puncture resistance.
And there's also the Continental Grand Prix Urban. This tire is faster and lighter still, and given how cheap it is, it's a good choice for shorter tours where mid-tour tire replacement in developing countries isn't a factor.
And for any single leg tour without a mid tour flight, tubeless should be considered. None of these tires are tubeless.
In building my current wheelset I went and did an oopsie. I wanted 36h wheels but could only find 36h hubs for the rear (not many of those on offer either). The front is 32h.
I chose ordinary crotchet rims because I was fairly sure I wouldn't tour with tubeless again after the last fiasco in sweden.
However now that there actually are really good durable tubeless gravel and touring tires available I'd like to use tubeless again. I'm pretty much sold on sealant and having a thicker touring tread helps massively in plugging a potential puncture. The problem is, there aren't any 36h tubeless rims. They exist, but not where I can actually buy them or they're too wide for the width of tires I'm using.
SO I need a new wheelset, but with nice hubs and TL rims AND alpine 3 spokes those things gets expensive fast.