Ok. The 8.4v 650mah NiMH battery pack turns the APC 5.7x3 at 14,900. It turns the Cox gray 6x3 at 12,600. It turns the orange GWS 6x3 at about 14,750.

I have an old Ace analogue Tachmaster II, it's not digital, so I'm reading the needle as best I can. My readings are within 100rpm or so.

As soon as my 9.6v battery finished charging I will re-test. I think it's safe to predict that the APC 5.7x3 will top 15,000 on this battery.

This actually out turns some of my old Babe Bees on 25% nitro, which did around 14,500 the last time I tached them.

Should I try a Cox gray 4.5x2? The problem is, this motor system is a lot heavier than an .020, so that's not a practical prop to use.