I'm Dualboxing 2 Feral Druids. The diagrams you've shown is exactly how it has to be done.
The benefit to it, and dual druids with similar specs/gear is that we trade agro around alot allowing me to just do white attacks and shred for maximum dps.

We're only level 42 so no mangle yet but that should be fun too.

On a side note, I'm also leveling an Enh Shaman to pair with my 70 paladin (will respec to ret when he catches up)

The synergy between the two is amazing. WF + Strength + Bloodlust and Blessings + Auras + Judgments is really incredible.

I consider each one about .75 dps and .3 healing... Well combined I feel like they're 100% of a dpser and about .5 a healer leaving me with 2 solid dpsers and a healer out of my two man team.

I'm bring this up because, 1) I cant imagine any melee dps multibox group without a Shaman (except for 5 feral druids maybe... since goa < wf imo). 2) Any Shaman would be significantly more powerful with a Paladin in tow.

So to me the optimal 5 man melee DPS setup would be Arms, Fury, Fury, Enh, Ret. I just did some quick math on it and the fire and forget healing (healing stream + judgment of light) would be about 616 healing for the group every 5 seconds. (This is not including WF and is assuming a 3 second weapon speed for everyone so the real numbers would be a fair ammount higher). So 5x might/kings and 5x str (from shaman) and double spell resists from auras/totems or crit aura from the pally... All in all i think its a much more solid set up than 5x or 4x warriors.

/end rambelings