Define "performance" first. A carb can make lots of horsepower at wide open throttle, but be a complete pig in the lower throttle positions/rpm ranges and "perform" poorly.
A PWK carburetor is technically a higher performance semi-flat slide smooth bore carburetor. This means it doesn't rely on a physical venturi to operate, which makes for smoother airflow and thus more volume than a similar bore size standard carburetor, which is what the PZ is.
In theory the PWK should perform better, but theory and reality don't always work the same. Good ports and proper tuning will always do more for power than huge performance carbs. True in 2 and 4 strokes. Properly sizing the carburetor is far more important than the type IMHO. On these tiny engines the difference between the 2 carbs wouldn't really come into play unless you are going to be pushing very high RPM to get into the peak power curve.
