Chinese spindles typically have a minimum rpm of 6000-8000. They won't have any torque at 1000rpm, and will die a quick death.

I've drilled 3 and 6mm holes at 5000 rpm with my SuperPID controlled router. I don't think I'd try any larger at 6000rpm. I often just drill shallow 3mm locator holes, and finish drill on the drill press.

A single flute "O" flute works very well in aluminum. For larger holes, just interpolate them with the single flute tool. 50mm deep may be an issue, though.