RE: 3500 RPM per volt motor ?
kV-numbers:
For DF, pylon etc you need high numbers, like 3000 or more. These motors also works in gearboxes for ordinary use in planes.
For sport/acro/pattern a medium kV number is good. Here you want to spin a "small" diameter propell with high pitch to get the speed needed.
For 3D and large sailplanes turning a large diameter propell on low RPM a low kV-Number is suited. 300-700 typically.