I was thinking of getting an air-cooled one, much simpler to not have the water-cooled system attached to the sled in some manner.
My thinking with the spindle wattage was simply just for overkill. I would like to change over to the 3/8" diameter, 1/2" shank cutter with the replaceable inserts like the one in this thread for my primary tool. I would like to try to do full-depth cuts with that, or at least 2 passes on 3/4". That’s where my thoughts on using a more powerful spindle came from. Looking over my notes, however, I have a 1.5 kw (2 hp) and a 4.5 kw (6 hp) spindle, so I’m not sure where I got 2.5 kw. Of those options, the 1.5 kw seams more reasonable, as it has the same power as the Rigid R2200. The 4.5 kw spindle definitely seems like overkill, although I like that it uses ER32 collets, whereas the smaller spindle uses only ER11.