Ive been through all this before, comparing the various models and balancing this and that.

the plus tours 37-622, 700x35 are about 900g, 890g. rolling marked as 3.5 out of 6
mondials 42-622, 700x40, are 650g, rolling 4 out of 6
supremes 42-622, are 490 or 590g depending on which one, rolling 5.5 out of 6

and the prices vary a lot too, although I imagine they are less expensive in Italy. Here, you are easily looking at 50-90 dollars canadian per tire, so it very possible to spend 200 dollars to find out how you like a tire or not.....

to me it comes down to how much you realistically think you'll be on gravel, and what sort of gravel. Regular marathons and similar with that sort of tread, works fine for me on nearly all kinds of stuff I ride on, and I also rode the more slick supremes on a lot of dirt roads, but they were not super rocky (where sharp edges could cut the supremes thin sidewall) and I could ride on it fine.

I can say that the supremes do roll very very nicely, and if one pays attention, are remarkedly good for punctures, but that depends a lot on rider attention and using common sense. I rode my 26x2 supremes through half of mexico, central america and across france and didnt get a puncture on the trips, but I realize this is perhaps an exception--and also, I was not riding on really rough dirt roads and very rocky, tough little trails , mostly on all sorts of levels of paved roads from great to horrible, and mostly "regular" dirt roads.