<i>"However, every trailing stop, profit target, and hard stop I have ever tested with it has shown a GREAT decrease in the expectancy and profitabiltiy of the system."</i>
I've run literally 1,000s of system tests and realized the same facts myself.
That said, do you find any hard stop that keeps average $$ profit per trade similar, yet greatly reduces max drawdown? You might find that hard stops shave a tad of overall profit BUT likewise slash your max historical drawdown OR the real one somewhere in your future.
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Stick with market orders in the ER. Partial fills on orders above 5-lot are the norm, not exception. Partial fills will kill you much faster than average slippage will.
Best Wishes