In my mind the most optimal setup is always going to be one extremely geared character.

There is no way to automatically pick up loot in this game. Sure, if you already RMAH'd most of the gear and can avoid 99% of the drops on the ground it goes easier.

Personally I find I spend a lot of time syncing them and a bit more time dealing with inventory issues such as selling / repairing / gear comparisons. I haven't spent much time looking at clear speeds and then dividing by 4 as my guys are still under geared. Basically my 150k DPS WD is carrying the other 3 at the moment.

Theoretically if you can clear Alkaizer in 30 minutes you multiply that by four. 2 hours. You'd have to come in lower than 2 hours for it to be worthwhile.