Speed boots should give bonus movement points equal to their enchantment (or slightly fuzzed as +1 to -1 randomly) on top of, or rather than, what they normally give.

Blessed speed boots give you additional movement points equal to their enchantment. (If their enchantment is negative, they subtract movement points, to a minimum of 1.)

Speed boots’ speed is gently nerfed to be better than intrinsic speed, but worse than temporary sources.