Using a Leslie efficiently and effectively can be quite challenge – to get the best result, you may have to adjust you drawbar settings to get the most out of your Leslie fast setting (or, alternatively, to tame it down). If you use the Leslie on fast on your typical Jimmy Smith setting (888000000 / 808000000), you will get a very limited, subtle Leslie effect, even with the rotors on fast; if you want the highs to swirl prominently, you will have to add the higher drawbars. To stay with the Jimmy Smith idiom, try 800000888 on fast, and you’ll see what I mean. You may have to adjust your playing style to get the most out of the more extreme settings.
Some players seem to like introducing some reverb before the Leslie to get a different sound, this is something to experiment with.