As a matter of verisimilitude, this discussion is stupid. My dog has 10% of my size and I simply cannot cover the same distance as him in the same amount of time. As Yoda would say, size matters not. Agility? Sure. Physiology? Probably. We're talking about fantasy races here, they're as quick as the designers want to describe them to be, and there's already a precedent for "as fast as humans" small races in OD&D. Also, if anything else fails, this is the kind of thing where applying a house rule is so easy that their change has no power at all to hurt your game. Next is the "play the way you want" edition, just do that.
Cheers!
Earl Boykins (a professional basketball player) runs faster than anyone in this thread, and can do it for an hour straight and while weaving through traffic.
So did Spud Webb, who won the NBA slam dunk contest.
So did Tyrone "Muggsy" Bogues (who played alongside a guy who was 28 inches taller than him).
Any yet you know what, all of them are short guys. Not just "short for the NBA", but actually short. I think Muggsy is 5'3"?
The tallest guy doesn't often win the short track race nor the marathon, either.
I get that "all things being equal, shorter should be slower," but we're not talking about an "all things being equal" situation here. We're talking about a base speed that is supposed to cover equally a 16 year old male athlete in top form, and an 85 year old woman with arthritis and breathing problems. We're talking about different SPECIES of humanoids which could have different physiologists from humans. And we're talking about situations of combat where adrenaline is pumping and obstacles vary wildly from encounter to encounter. And we're talking about bursts of speed, 30 seconds to a minute of time for combat, and not marathon overland speeds (which I would agree should vary between the races). But SOME halfliings should be able to move five times as fast as SOME humans for instance, particularly in a burst speed of 30 seconds.
So all things are not equal, and the range of species and ages and levels of fitness and health and events occurring vary so wildly that any discussion of "verisimilitude" really rings false to me.
Like I said, I vaguely would prefer a slower speed for the smaller races, but only in a mild way, and mostly because of recent tradition. But, it's not because it messes with the appearance of being true and real - it's perfectly believable to me that an average halfling adventurer moves as fast as the average half-orc adventurer during 30 seconds of combat, because of the wild swinging variables involved in movement speeds I mentioned above.