For my nightclub work I usually hit up around F9, 1/4-0.4 ISO 100 and maybe 2/3rds flash power, use flash on manual instead of ettl then you know 99% of time time you will get a good exposure.
DJ Bobbytron by James E36, on Flickr
DJ by James E36, on Flickr
Jikay DJ by James E36, on Flickr...