I put a 54mm front tire on my cross/gravel bike (rear is 40mm). Wow, what a difference. Front forks tend to have lots of room, so there is often the option of going monster cross big on the front – even if the rear won’t go that large. It really changes the personality of the bike.
I ride 28mm on the front on the road, and 40mm grave. The 54mm (Thunder Burt) really makes the bike feel like a ridged mountain bike, adds more traction, increases trail, adds to stability, slows down the steering, adds a lot more cushion (low 20's psi), makes the bike feel more like a truck, and a makes soft sand much more rideable.
Speed wise it rolls well, and can cruise on a flat road within 5-10% of the speed of the 28mm race tire. It also accelerates like a mountain bike (i.e. slowly with effort) and has a bit of a gyroscopic effect. It tends to slow everything down, which is good for gravel.
I have it on a 700c wheel, but I think clearance wise and to match the 700x40c tire a 650b 54mm version would be better. But on my bike the slacker head tube angle by the large front wheel isn’t a bad thing.