The diversity is better served with a 5 man team, that's where you see the most benefit. with less than 5, you have less potential DPS. With a smaller team, you would probably be attempting slightly smaller pulls than a 5 man team (unless you are really well geared)

You already have 4 accounts, and are doing a diverse setup, so I'd just bite the bullet and roll a 5th. You could easily double up on an existing DPS class if you wish, to keep things simpler. Or you could go the 5 unique class route, and have more utility.