I reckon the Horizons are as big as I'd go on a 650 gravel/all road. Anything bigger, and things will start to get too squirmy and sluggish.
I've just started using the Gravel Kings. Still finding that pressure sweet spot, but they have a similar feel to the G-ones. 350g to boot.
Yeah- it's strange- 38 or 60 I think, which are the "big ones"- have a set of them as well but think too big for this bike...