I don’t find it comfortable to spin at 120 for long distances.
Why would you have to?
First of all just because you have a tail wind it doesn't dictate that you have to go as fast as you can. You could just take it easy. That said
even with a crazy low high gear I didn't notice much of a problem even when riding with a strong young guy on the ST. I was running na 87.8" high gear (39/12). According to a gear calculator that means that I could spin a measly 80 rpm and go 20.88 mph. At 100 rpm it would be 26.10 mph. At 120 it would be a whopping 31.32 mph. Heck you could even noodle along at 60 rpm and still do 15.66 mph. This a tour after all, so if you aren't in a hurry that would be an option.
Also almost all of the newer bikes have an 11 or even 10 t cog and a bigger than 39 t ring. Even the 1X bikes have a higher high and a wider range than I had on that ride. Some of the gravel bikes have something like a 10-50 with a 42T ring that gives a decent high and a decent range (actually better on both counts than I had on my heavy triple touring bike).
I plugged in the numbers for the 10-50/42 of one of the new 1x gravel bikes and came up with a gear inch range of 23.2 to 116. I don't find that limiting at all. Granted some will find it limiting on the low end, but most won't have any trouble with using a little smaller ring given that it has a 10t cog. You could get down into the mid teens and still have a decent high gear IMO.
Edited to add that gear spacing may be another issue, but the numbers look okay all around with some of the 1x setups given 12 speeds and really wide ranges. Nothing is perfect, but they look pretty good to me. Then again I never felt the need to find exactly the right gear. I can spin a little higher or lower cadence or go a little faster or slower, especially when touring. A few gear inches one way or the other just isn't going to kill me.