Hey Kelly,
regarding power, more of it means higher speed to achieve the work. Once you will cease to work and instead watch your “robot” doing the work for you, the more you may want it to become faster. More power also means more torque at low speed.
Once the 80 mm spindle holder was out I ordered it and I came accross the question
whether to buy a 2.2 kW spindle with ER16 or with ER20 collet. The first takes tool shanks from 1-10 mm and the latter from 1-13 mm, which would mean half-inch tools. But since at first I did not expect to use tools larger than 8 mm, I was unsure. I asked the manufacturer and he answered, the spindle with ER20 collet has larger bearings and a stiffier shaft. Larger bearings means longer life. Stiffier shaft means more precision. Also one should take into consideration that when using tools with a larger shank, the thicker the shank the stiffier the tool and so the longer the tools you can use – and thus the deeper the pockets you can mill into your workpiece. So I went for the ER20 spindle.
I agree.