Just for consideration, I have a Trek Crockett 7 Disc. It is Trek’s modern alloy CX bike and very light, but also pretty bomb proof. I’ve race three seasons of CX and multiple gravel races and it has been really solid.
Anyway, to answer your question(s), I have done some 4+ hour rides on my Crockett and been super comfortable. In fact I will often choose it over my road bike for long stuff because it is more comfortable and the wider tires make Texas back roads way more fun.
I can’t find confirmation, but I have heard the Crux can take pretty wide tires (up to 40s?) which would sway me to it. The Crockett can take 38s which have been perfect for the stuff we race here in Central Texas. So it is worth checking on tire clearance options if you want to do any hardcore gravel. I know quite a few folks who race gravel on a Crux. Some CX bikes are limited on tire size. The Trek Boone can only take 35s on the back, for example.
I would also check on Chainring compatibility / max sizes, and/or if you can put a double on in future. I use 1x for gravel but did have a race recently where we had a tailwind and I got dropped because I spun out of gears. Majority of the time 1x is perfect though.