@deckingman
Yeah - 6mm belts can definitely drive those masses!
My experience for the past year has been that as long as the pulley is mounted as close as possible to the motor, no bad effects have been noticed on my largest machine that I haven't upgraded to double shear yet. On the smaller version I made of it, I made a double shear support that floats with the motor casing to keep it from bending and causing issues. So Far, So good, and it spins plenty fast and tensions as high as you'd like it. 20210610_075332.jpg 20210610_075321.jpg
The belt dust is from when I had a light interference with the belt from the edge, which I fixed with a deburring tool. Now we're at low clearance 😄