I ordered a pair of Marathon Supreme Microskins in 700x35. I'm looking forward to the direct comparison with the Gravel Kings. They are quite a bit heavier. Although I know it really doesn't matter my inner roadie wouldn't let me buy the 700x40's because of the weight.
As an added complexity I really like running tubeless tires. There aren't many tubeless options when you get larger. I did find a couple of interesting things though. First, it turns out Panaracer just released a couple more variants of the Gravel King, at least one of which is supposed to be more puncture resistant (which I assumes means thicker/tougher). Second, I found the Vittoria Terreno Zero which looks like it could be an interesting choice. Available up to 700x38 and tubeless ready. About the same weight as the Marathon 700x35.
https://www.vittoria.com/us/terreno-...nd-gravel.html
I'm sure the perfect tire is out there!