I run the smallest pulley I can find which is the 614 size
The torque multiplication of the smaller drive pulley is very noticeable. I was under the impression that Reliable shipped their motors with 50mm pulleys. I was almost correct, Keystone Sewing ships motors with the small pulley.
I feel tools are not a place to skimp on cost. I'd rather wait a little longer until I can afford a quality piece than have to purchase it twice in the end.