What percentage of the Ideal Stirling Cycle Can Be Harnessed

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Does anyone know what percentage of the Ideal Stirling cycle can actually be harnessed? Have any real world devices managed to harness more than 90% of the ideal Stirling cycle? Clearly, a sinusoidal piston motion is problematic to harnessing more of the ideal stirling cycle. Can other mechanisms harness more of the cycle?

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Maybe my question doesn't even make sense. With a 100% efficient regenerator and a 100% efficient mechanism, deviations from the ideal stirling cycle may not reduce efficiency. However, I'm not sure about this.

[tomostre]

you saw them videos suggesting a rotary displacer? also running a search for ideal stirling cycle showed a rotary sine slotted "cam", that might be pertinent to your question. Also, the ross yoke provides greater movement of piston then the crankthrow, making the whole thing perhaps more efficient - at least that is how i understood andy ross' idea behind the patent.