The Yamaha CS-10 VCO is based on the IG00153 chip, which is a linear VCO. Here are the control voltages which are produced by the keyboard (with pitch-bend centered).
C1 = 0.25V
C2 = 0.50V
C3 = 1.00V
C4 = 2.00V
The Pitch-Bend is +/- 1 octave, so the maximum range is 0.125V - 4V (ie. 5 octaves).
I have verified these values on my own CS-10 unit.