Regarding measuring risk/reward of a system: Maximum drawdown is not a very good measure for system risk. Also it is not a good predictor for future drawdown. There is math logic behind the popular saying "the worst drawdown of a system is yet to come".
We look at backtests trying to get an estimate for a system's future behavior with an underlying assumption that the statistical characteristics will remain the same. But the maximum drawdown is not a good representation of the statistical distribution of trade results; it expresses just a single path of trade that occured up to this point.
A simple example: The following trade results could come from two systems with similar statistical characteristics:
A. +2 -3 +2 -1 +2 -2 +1
B. +2 -2 -3 -1 +2 +2 +1
In evaluating the potential risk of a system, measures that look at the statistics of trade results and not a single path would be more predictive. Downward Deviation, or Downward Deviation of rolling periods would be a much better measure for system's risk. Sortino, or even Sharpe Ratio would give a better prediction for future system risk adjusted return than (past profit) / (maximum drawdown).