IMO, the only reason to get a 2.2kW spindle for a Shapeoko is that it’s required to get a cheap (Chinese) HF Spindle that supports 1/2" endmills (which you likely don’t need). Lower power and smaller (but more expensive) quiet electric fan (rather than shaft driven) air cooled Italian HF Spindles are available that support 1/2" endmills.
If you’re only cutting wood, there are lots of router bits with 1/4" shanks you could use and get by with an apparently decent 800Watt Chinese HF Spindle.
The following shows that 2.2kW (2,200Watt) and 800Watt HF Spindles are capable of 7.7475 and 2.8173 lb-in of torque respectively. Dividing those torques by half the endmill cutting diameter will determine how much cutting force the machine would be subjected to at those torque levels. Stock Shapeokos can support a maximum of about 18 lbs force, and likely a usable force of around 5 lbs. So 800Watts should be more than adequate.
