You have another thread going with some regard to this same issue. So as I said in that thread, these "aggression" issues will continue for some time. There is a hierarchy that needs to develop and it will take some time to do so.
5 discus in a 60 gal
is perfectly fine however, the other tanks you've seen, (50 and 55 g) look bigger because their overall length is larger and most well state that length is better. A 50 and 55 has a 48" (122 cm) length where your 60 is only 39" (100 cm).
Depending on age and overall size, Discus NEED lots of WC
's. As I've pointed out before, there are a few reasons for this. Juvies require multiple daily feedings, young adults a little less, and adults even less. WC
's coincide with this simply because that's what helps them grow and mature into large (6-7" +) sized fish. By not following these methods, I'm afraid you fish will remain stunted at around 3-3.5". What will happen then is their organs will grow to a size larger than they can handle and die earlier than their intended life expectancy.
Also, it doesn't matter where they come from. It is my opinion and experience that ALL fish need QT before going into a tank with any others for a plethora of reasons that I won't get into again.
These items that I'm listing are all based on facts learned from experience and failure. And lots of RESEARCH !!! I'm not criticizing you for what you've already done but I have tried giving you plenty of advice and it's yours to do with what you'd like. Should you choose to take it and use it to your advantage, I'll help you any way possible. If you wish to ignore it you're on your own. They are very easy fish to keep. Just a little dedication and devotion and you could have some that look like this.
A 6" Eruption Leopard and 6" Pigeon Blood.