I guess it could depend on how far back the truss (or whatever they'll be hung from) is from the stage. Our lights are about 14 ft from the stage, and about 14ft high. We have 6 par64's running off of a Stage Setter 8. We dont have any problems with it. I think a Par56 will do the job, but a 64 could do it better, lol.
-Chris-