What I'm going to do now is to mine Monacoin here on MPH for three days, then on suprnova for 3 days and then I'll compare average hashrates and profits.
Bad approach. If you want to compare 2 pools, you have to mine in parallel. Otherwise, the results are not comparable as the net difficulty in 4-6 days can be completely different from days 1-3!
You are right, I have not considered difficulty change.
I'll do next: I'll run two instances of ccminer with 2 GTX 1070 each: 1. MPH, 2. Suprnova
24 h should be enough to make conclusions.