Being faster than 100 speed makes staves recharge slower, e.g. staves zapped by a 200 speed character will take twice as many turns to recharge. On the other hand, being slower than 100 speed does not make staves recharge faster. Turns spent on the world map do not count any more than turns spent in dungeons (which would make sense if high speed is counted as less time). I think it would be better if staves didn't have any dependence on speed, as many of the effects (stat boosts and satiation) are based on turn timers that don't scale with speed, but in any case, the behavior should be more consistent.