Hi peteeng,
with my small (800W) spindle I use predominantly small tools, 1/8" and smaller. Ocassionly I use a larger 6mm tool, although its less about increased metal removal but decreased number of passes
and therefore cycle time, the wee spindle has such low torque that trying to take thicker chips will stall it.
If the job warrants it then I swap over to my other spindle (1.8kW) and run 12mm and 16mm tools....then the chips fly off.
Craig