We've done many high end camera installations and the twisted shielded pair travelers have worked great. Is your client installing card readers for security as well? If so, I would recommend to hang a separate traveler to include cameras and the card reader. This way it's separate from the elevator controls and you can run the traveler all the way back to your security console (minimize slice points). Then just wire the individual wires to a CAT 5 adaptor or splice right to a pigtail connector.