here is my data from 24 hours of mining for the monday payperiod comparing hashcows with middlecoin.
method: 2 identical miners, each with two R9 280x, running with no crashes on client side. both pools payouts enumerated by withdrawal of all deposited coins, once per day.
hashcows: 0.0168xxxx btc
middlecoin: 0.0480xxxx btc
I can tell you from experience that 24 hours isn't enough to tell anything. Middlecoin has good days and bad days just like the other multipools.