Mine is 1:1 ratio. Torque has not yet been an issue. I typically only run the main spindle between 30 and 60 Hz (800-1700rpms), I have on occasion over driven it to 2x's it's rated speed, but not very often. Bellow 800rpm I still have my back gear, and above 1700rpm is precisely why I am building my high speed spindle attachment (lower down in this section).
I find the range I have available on the main spindle is pretty much perfect for any larger tooling that I would need the HP for anyhow. W/ the high speed stuff, I am typically working with engraving cutters and router bits and hit 10-12K rpms pretty regularly. That is well beyond the capability of the factory spindle bearings anyhow, so no use trying to overdrive the spindle motor or providing pulley overdrive to hit these kind of speeds.
Mactec54; The pictures you posted of your head conversions about 1-1.5 years ago are what inspired me to take this route. I know it is not as pretty or shiny, but it was inexpensive and solved the beat up varispeed problem. Many thanks for posting the original photos and for planting the seed in my head
Later,
Jason