Bit_Bucket_07, I think you are referring to NFPA 70 300.3(C)(1). That states that the limitations are based on the maximum voltage in any of the circuits, not the maximum insulation rating of the conductors in the mixed circuits. In fact, the Handbook makes a point of saying that it is the applied voltage not the conductor insulation rating that matters.
Having said that, I would separate circuits of different types if I could. But, if you have to mix functional types in a pinch, be very careful about shielding the low level conductors. I would go as far as shielding the power conductors also, making sure to ground the shield of the power cable on both ends.
Look at it this way. If it was completely impossible to run mixed conductors in close proximity, single cable servomotors like the Rockwell VPL series wouldn't exist.
Keith