An enhanced LBT procedure (200) mitigates unnecessary delays in delivering transmissions between User Equipment and base stations over unlicensed spectrum. A UE or base station selects a particular CAPC corresponding to an intended transmission (225) based on an intelligent mapping of different types of transmission payload (e.g., transmission payload other than or in in addition to pre-defined, QoS-related UP message data payload) to different CAPCs. Most (if not all) of the mapped CAPCs corresponding to the different types of transmission payload are of a higher priority than a lowest priority CAPC (212-222), resulting in channel access procedures that are more commensurate with respective transmission payloads. The intelligent mapping may indicate different priorities among different types of transmission payload and/or different types of messages, and/or may indicate which type of transmission is to govern selection of a CAPC when multiple types of transmission payload are included in a single, intended transmission.