I think the game should track permanent and temporary speed separately such as is done with other stats and use only the permanent speed rating for determining experience gain/loss.

This would prevent the exploit of slow monster for massive experience gains and regulate it to simply another escape method.

As well as negating the experience loss from potions of boost speed.



(Note: I myself rarely use either of these so am not greatly invested in whether it changes or not, but I think it is a sensible solution to ~75-80% of the conversations which come up regarding speed.)