That seems like a pretty big space, especially with those 14 ft ceilings. If it were me I would get the QS8's just to be safe (but I may just being over-cautious). Keep in mind that I haven't heard the QS4's. You might want to give Axiom a call or send them an email.

Hopefully someone who owns QS4's in a large-ish space will chime in with their experience.