RE: 1/2a speed delta
The MAS cut down to 4.25" works well on the AME. If you want to pipe time the AME, I would guess that the APC 4.2-4 is a good match,but this prop needs an engine that can really spin it for it to put out. If you have the airframe to support the speed, keep taking away diameter [of the MAS 4.25-4]. This little delta might even do OK with less than 4" of diameter. If you buy the MAS twin pack, it will cost about a buck to find out.