I received and installed the 500GR, but I haven't gotten the 2" pulley yet. It does have a lot more torque on the low end than the other servo motor, and I'm able to do 1-2 stitches/sec by barely pressing the pedal. However, it's still very fast with just a bit more pedal. Still, a good investment I think. Hopefully the 2" pulley will make even more improvement.
I tried adjusting the brake, but could not break the spring-bolt by hand and didn't want to strip it.