According to the CK61 manual, you CAN adjust the rotary speed using the Effects panel and Trm/Rtr. I don't own one, so if a member who has one could check to see if you can indeed adjust the rotary speed, that would be great as it seems the too fast speed is a sticking point with the model. Unless I"m confusing this with the tines rotary effect?
Effect>Trm/Rtr> Simple Rotary Simple rotary speaker effect. Turn the [DEPTH] knob to adjust the volume and distortion level, and the [RATE] knob to adjust the rotation speed.