Can't comment on the Chinese 3 kw spindles.
I do have experience with Sherline spindles (both with regular and their "high speed" pulleys).
While the regular speed spindle was just fine, the motor got very hot. The spindle became very hot at 10k rpm even when bearing pre-load was adjusted per Sherline instructions.
Have you considered the Taig ER-16 spindle with their 1/4 hp motor? I use that now instead of my Sherline. The Taig motor runs cooler, the belt changes are easy, and the spindle itself seems to tolerate 10k rpm much better than the Sherline spindle with "high speed pulleys".
The Taig cuts aluminum very well. Works ok on wood but the rpms are a little low for that.