We went foxhunting at East Fork Stables on Saturday. I was riding "Second Field" (we follow the First Field that follows the hounds). We covered 12-14 miles in just under 2.5 hrs. That's a fairly aggressive pace. Perhaps 4-5 miles was on a hard-pan gravel road. I'd say 10% of our time was at the walk, 40% in gait, and the rest at the canter/gallop. Hunting East Fork means a lot of time in the woods (maybe 1/3) where the trails can be anything from well kept to dirt tracks. Our field did not go into the woods; First Field did and scared up, among other things, 4 LARGE wild sows and 40 or so piglets. Last time it was a couple of black bear. Coyote are common. Hunting East TN is nothing if not diverse.
I noted no issues doing lots of gaiting and galloping on the hard surface road. No lameness/sorness issues afterwards. My mare is trimmed to anatomical correctness and shod normally to protect the trim. When we are gaiting I want her in correct form (not a "show" form, but carrying herself and fully engaging her back end; I don't want her "pulling" herself along on her front legs). I also keep her "together" when moving at the canter/gallop. If she gets "strung out" she loses efficiency, balance, and can take a spill. That would be very bad for both of us.
Fast work on a hard surface is not a death sentence for the horse.