I have been quite happy with the GF-001 from Velobuild. I've had it for a few years now and it's been pretty solid. I've done several gravel races, few CX races, and I also use it as my winter road bike. I've been looking at newer frames that have a little more tire clearance and a round seatpost, but not liking anything but maybe the tantan G047 or LightCarbon's latest offering, and I'm not digging the full internal cable routing thing.
This frame is still avaiable and I believe you can get it from spcycle or tantan as well. It comes with replaceable dropouts, so you can even switch from QR to Thru Axle in the rear. I raced 40mm Michelin Gravel Power tires without issue. You can probably fit 42s on there, but for me, the limiting factor was my front di2 derailleur rubbed on the rear tire. If you go 1x or maybe a mechanical front mech, you could probably go bigger than 700x40c. The only thing I don't like about the frame is the seat post is not round. I've had the post slip twice, both times after doing maintenance where I needed to remove the seatpost. Even with carbon paste, the wedge design is a little finiky. Once it gets seated, it doesn't move, but it's still an anoyance.