I trade systems across a number of commodities with time frames ranging from 5min to Daily.
Portfolio growth, although ultimately the goal, is not the best measure of a systems merit I feel as that really is dependent on leverage employed and says nothing of the characteristics of the methodology.
I work to develop non volatile return and high % of profitable trades, this makes trading a system so much easier on the psych. At the end of the day the hardest part is following, to the lot, the sigs and getting execution right. It does not take much testing to realise how slippage critical systems are and how working for that extra tick makes a significant difference over time.