HI Gary, The opportunistic rate selections are only supported on the AP7161 and AP8163 as per the guide.
Opportunistic - Configures the opportunistic radio link adaptation (ORLA) rate selection mode The ORLA algorithm is designed to select data rates that provide best throughput. Instead of using local conditions to decide whether a data rate is acceptable or not, ORLA pro-actively probes other rates to determine if greater throughput is available. If these other rates do provide improved throughput, ORLA intelligently adjusts its selection tables to favour higher performance. ORLA provides improvements both on the client side of a mesh network as well as in the backhaul capabilities. Note: The ORLA rate selection mode is supported only on the AP7161 and AP8163 model access points.