I have 2 belt ratios utilizing J6 poly V belts low gear is achieved through a 1:2 belt ratio (150-3000rpm) and high gear is achieved through a 4:3 belt ratio (3000-8000rpm) Rigid tapping was never a design requirement for me but was a 'could be nice to have' feature. My goals were to increase the maximum rpm to at least 7500rpm and still have enough torque in the low end (500-2000rpm) for machining steels. I can't take credit for the idea as I copied the German fellow referred to earlier in this thread who copied the fadal belt actuator design. I will give some background info into my spindle motor design and post more pictures/videos as I assemble it on the mill. That's when rigidity really starts to be a problem. That involves lower RPMs obviously and bumping up the chip load to prevent work hardening. I've even been able to cut 303 stainless which isn't quite as easy. Yeah, it doesn't cut very quickly but it will hold <0.003in all day long and give a nice surface finish with a descent high flute end mill at 10krpm for a finishing pass. I'm usually using a 3/8 or 1/4 roughing end mill, around 5-9krpm, and feed rates of 20-30ipm. When I cut aluminum on that machine I'm usually doing MRR's of around 0.5-0.8 cu in/min, which isn't a lot, but its good enough for a hobbyist with an 80lb machine.

When I first got my Taig I didn't think it was capable of very much and after spending about 3-4 years with it I've learned that you can do a lot with with a 10k spindle and some reasonable feedrates. but what a learning experience! These smaller mills are far less forgiving than something thats 1,000+ lbs with lots of HP's which really taught me a lot about feeds and speeds and best practices to get the most our of a machine. I went from using Bridgeports, Haas toolroom mills at uni to a Taig mini mill at home after I graduated. My home shop experience has more or less come to the same conclusion as yours.

Taig mill servo motor