Thanks for the replies – a few answers to suggestions / comments so far:
I’ve done my fair share of riding MTBs over the years and have been re-discovering the joys of drop bar bikes of late.
I don’t “race” any more but I’ve done the odd Adventure Cross CX style sportive and similar events. I ride a GT Grade and 35c is the max tyre width that’ll leave any mud room. The “Gravel Specific” tyres I mentioned come with puncture protection layers which CX race tyres don’t as I understand it. I’ve not tried proper CX tyres on my Grade, but have been put off by plentiful reports of multiple punctures when riding Cross tyres away from the race circuit, as they are built for speed, grip & lightweight, rather than robustness / durability.
I’ve done some fairly rugged rides on 32c with not a single flat, but would like a bit more airspace for extra grip / comfort / protection.
I do have some 35c Landcruisers, but they are waaay heavy for longer rides, especially where a lot of tarmac is involved.
I can get by ok with what I have, but it’s frustrating when you can see riders on what appears to be exactly what you want in the USA and you can’t buy here.