Hi H20LOVER.... well, I'm surprised to hear that an XP3 wouldn't be enough flow for your 60 gallon cube. It's roughly a 24x24x24 inches dimension, right? Is there something unique about it that would have caused some other person to say XP3 wasn't enough flow?
And sorry - I can't answer about the FX5. I use XP3 on all my tanks; one of which is a 50 gallon and one of which is a 75-gallon. I use 2 XP3's on my 125-gallon cichlid tank. So I can't tell you how the FX5 would be, never having used one myself.
you could tone down the flow on a fx5 if it was to much by doing a spray bar or two with more holes = less current but same flow i thought of putting my fx5 on my 40b and just dialing it in but thats me