Yeah, whether 38mm is wide enough will depend heavily on the quality of the gravel/dirt paths you ride. I took a friend on one of his first gravel rides last weekend and he was even running 42mm tires at a reasonable pressure (ie, not too firm), and at the end of the ride he told me he was pretty sure gravel riding wasn't for him. The main factor was he found the descending over rough rocky sections to be too harsh and was used to road descents being the times when he could recover a bit. Bigger tire clearance gives you the option to run wider tires at lower pressures, which can absorb more of the rough stuff.