Both QS4's and QS8's are very sensitive 94 and 95 db respectively and your receiver or amp will drive them easily and play loud. The QS8’s have a lower frequency response than the QS4’s (lower bass) but not much. I like the QS8’s they are wonderful. I’m sure the QS4’s are great too. I don’t think you could go wrong with either model.
Are you getting an entire Axiom setup? I would try to get speakers that are well matched. For example the Epic 80 uses a M80’s, VP150 and QS8’s. The Epic 50 uses M50’s, VP100 and QS4’s. I believe they are all matched up by wattage and frequency, I could be wrong though. The dimensions of your room will help.
