I’ll be DMing some more 5e soon and I want to take the opportunity to try some different ways of playing (I’ll post my own suggestions as comments so they can start their own discussion threads). What alternate rules have you tried that you thought worked well? They can be larger changes to the game or little QoL tweaks (though if you can respond to the suggestion with “at this point just play [different game] instead” then that’s probably more than what I’m looking for!)
I do something similar to Sprint, basically, you can move at double your speed for a round (so 4x total, dashing) but have to roll a Con save or take a level of Exhaustion. Each time you use this ability without resting, the DC goes up by 5. (Starts at 10.) Which feels about right, IMO. Lets a max-level Monk/Barbarian match (or exceed, with certain feats/races/subclasses) Usain Bolt for speed, but only for a short duration, even if they have a superhuman constitution.
150ft/round is approx 13.2 sec per 100m which is very achievable for someone who’s athletic. I’m not worried about max level barbarians, monks, or tabaxi being significantly faster than is plausible in reality: it’s fantasy. Sure, imposing some kind of exhaustion penalty makes sense, but 5e rules for exhaustion are pretty severe, and the point is to not sideline characters who happen to be a bit farther away when combat starts. IMO giving exhaustion would just be another barrier to my players having fun, it would defeat the point of what I’m trying to achieve at my table. But if it works for you, that’s great! I’m sure tables that want a crunchier and more realistic game would appreciate your version