Varies from person to person. Depends on how efficient you are throwing with a crow hop and how efficient you are throwing off a mound.
Generally, people will throw a bit harder off a crow hop than off a mound but there are certainly people who throw harder off a mound than they do when crow hopping.
If you throw significantly slower off a mound then you aren't getting the most out of your motion off the mound.
My guess, and that is all it is, is that most people throw 1 or 2 mph slower off a mound.