Julien has mapped a couple of insightful spindle/VFD threads…
For noise reduction, water cooled is the way to go. I would have gone 800w but I had a tough time finding an 800w spindle at the time, so I ended up going 80mm 1.5kw - water cooled - 120v (w/HDZ). The cutting noises are what they are, but you don’t hear the spindle itself. If you have cash to burn it’s definitely a nice upgrade: quieter, more precision, PWM controlled, etc…