I have my Altums with my Dantums in a 65g 3 foot tank for a year now no problems .There are about 15 angels all over 6 inches at least now .
Likewise I have 12 discus in a 65g 3 foot tank and they are growing well. A couple of the discus are easily at the 5 inch mark now .
They both might like a bigger tank but IMO the height and volume is how the group manages so well.
65g is a good volume of water .Others may like the foot print of a 55 or 75 better but space is key in my fishroom and both the 3 foot tanks are in the middle of the room .
No room for 4 footers there ..