Increasing speed through a skill is an overkill. I've already seen enough of orcish warriors running across the entire field at speed 9 in the original game; thank you, but we don't need that kind of mess. One skill that provides a speed bonus is enough (it's possible that this bonus won't stack with the corresponding artifact, meaning you won't be able to increase speed to +2).
With a +2 speed bonus, infantry almost turns into flying units, which looks about as bad as giving all melee units the ability to shoot. Archers should remain archers, infantry should remain infantry, and flying units should remain flying units. Although it's impossible to completely avoid large bonuses (for example, there are mini-artifacts that provide +2), where possible, such things should be minimized.