With dual mining you need an adequate amount of core overclock or higher power limits to support it vs mining ethereum solo.  

When I was testing with mining ethereum solo, I could pull off 50% power limit without significant hash rate differences. With my calculations including power consumption, the lower the power limit the better. If I attempted to dual mine with that low of a power limit, the ethereum hash rate took a nose dive and I couldn't use a 50% power limit anymore.

The increased power consumption is something to consider when considering the profitability. It wasn't worth the headache of fine tuning for ~10-15 cents more a day.