Hi Jon,
I have been testing my new RST-135E with various scopes that I have. In summary: with a fully loaded Takahashi FSQ-85EDP, at 11kG total weight, I use the mount without counterweight ad the mount operates flawlessly with a total guiding error in the range 0.2" to 0.4". With a heavier fully loaded Takahashi FSQ-106EDX4 scope, at 16kg, I use the small RST counterweight and I get similarly small guiding errors. Under windy conditions, the guiding errors change little going up to 0.3"-0.4" only, as the mount motors have a very large torque and handle the lod firmly.
This is a fabulous mount.
Best regards,
Jose