ifHighSpeed for 10 Gb/s port-channels

Hello, can anyone confirm why IF-MIB::ifHighSpeed should return 0 for aggregates of 10 Gbit/s ports? My google-foo led me to several topics on "use ifHighSpeed to 10 Gbit/s", but none is clear on 10 Gbit/s aggregated. So far I could only find references pointing to IEEE Std 802.1AX-2008 clause 6.3.1.1.16 (aAggDataRate), mapping to IF-MIB::ifSpeed, which is locked in 4,294,967,295 (Gauge32). In this same standard it is very specific about ifHighSpeed: "Set to zero.". Or, more directly: how can one find current speed of a 10Gb/s+ link aggregate port? Please, answer me off-list and I promise to summarize an answer... :) Thanks in advance. Felipe