Ok, tried turning the PSU down as low as possible. Unfortunately, 10.5V was the lowest and the ESC didn't seem to like it a great deal so it would appear 12V is the nominal. That's still 54,000 RPM. Though, I do think it's considerably less than that because 4500RPM/V is the no load speed and it's only a small motor so I would imagine that under load, even just spinning the spindle it's probably 5-10K less.

Anyone know of any brushless motors that can be had cheap that have a 3mm shaft with a reasonable KV, say 2000KV?