Thank you for the excellent data. I am considering removing the 8kHz sample rate from the available rates for two reasons:
1. The analog filters roll off around 1kHz, so sampling at 8kHz does not give you very much more information than sampling at 4kHz.
2. There is a sad interaction between the radio interrupts and the data ready interrupts that causes corrupt sample data when using 8kHz mode. I have not fully diagnosed this, but I remember seeing it crop up occasionally even in the very early days of development (2014).

Let me know if you have a strong opinion on this, thank you again!
~James