I am in the market for a adventure road/gravel bike at the moment, being an advocate of try before you buy, im having trouble as no-one seems to have stock in an actual shop that I can go and have a look at/try.
all points made about tyre clearances and frame geometry are valid observations.
for distance, I would imagine of you're not an out and out racing cyclist, I think the gravel/adventure type thing would be fine.
as others have said, tourers are also similar but I have a tourer, a Dawes Horizon. it is as smooth as you like over paths and roads but it rattles around off road on tow paths etc. its a great bike but I think the gravel adventure would be a little beyond what I would like to put it through.
I have a genesis equilibrium and a day one, both great bikes also but the equilibrium has 28mm contis on and I would not get much bigger tyre with a decent tread on that. the day one is great along tow paths and muddy flat fields but its hard going on anything with a slight incline in the wet. the day one would be a very comfortable bike over distance, it has massive clearance for up to 50mm tyres (check this before you hold me to it) but I would need more gears, hence the Croix De Fer from the same brand is on my list.