I have gone and done this. I have 2 identical 2.2 MH rigs that I am splitting between hashbros and middlecoin for a head to head test. Will let it run 7 days and report back next week. Currently, hashbros is estimating my earnings at 0.008329 btc/MH/day but that is fluctuating minute by minute.
Annnnd... I'm back. Putting a stop to this experiment. Not waiting a week, 6 hours was enough to know this won't hold a candle to mc. Over time, hashbros earnings dropped steadily down to 0.0055 btc/MH/day. It's curious that hashbros has a profitability index yet they don't seem to mine the coins that are most profitable.
I will promptly stfu now. Maximum payouts trump everything else.