Just my oppinion but I think it is best to initially take leveraged ETF's out of the equation when searching for the optimal use for a given amount of capital.
Otherwise the test will probably indicate it's best go with TNA/TZA only for maximum gain.

The problem I see with that is that this is based on historical data. The maximum drawdown of any system lies in the future and is unknown.
Risk of ruin is probably quite high going all in on TNA/TZA even tough historical tests show it maximizes profit.

Instead of trying to maximize gain it might be better to maximze the MAR ratio. (MAR = CAGR / Max DD) This way, risk is taken into account.
My guess is diversification in systems leads to a higher MAR ratio and to a smoother equity curve. I believe that it is safer to use leverage on a diverse portfolio of systems (either by margin or leveraged ETF's) than it is to do so on a single system, no matter how great historical backtest says that system is.