I've been running the Zinger 16x5 cut down to 15 dia. and modified according to 3Dreaming on my Ecstasy w/ ST90, Mac header and tune pipe. I was flying a APC 15x4W originally at 11,400 RPM. I ran the modified Zinger last weekend and it ran at 10,600 RPM. I swept the angle back some more to be 1" from the tip, radiused it, then thinned the blades. This prop ran in the high 11s (I think - not quite enough light for my tach yesterday, but obviously higher RPM than the APC). It flew great. Still not the pulling power of the APC, though great throttle response!
Kevin