Greetings,
I would interpret both datasheets as suggesting use of a PWM (i.e. digital) control signal. The technique of using an analog quantity (voltage, resistance, etc) mentioned in the linked Comair resource is less familiar to me, and as the document itself suggests (“…Each fan is different…”) it may be something of a hack, whereas most devices respond quite predictably to changes in a PWM duty cycle in spite of subtle differences in their interface mechanism.
You may find this this resource on related topics useful. As for the question of determining what analog voltage applied to the control input would produce full-speed operation of the part numbers mentioned (or if this technique is even valid) that would be something a person would have to characterize oneself, as it does not appear to be part of the product specification.