(Edited as a follow up on this topic after conversations with the customer)
One of the weaknesses of the BB60C is the low Dynamic Range/SNR. It is the result of amplification in the RF section to reduce residual signals.
Depending on your settings we would expect a maximum ~48dB SNR in a given IF band. (measuring SNR at 40MS/s IQ) It may be less in some configurations (as you mentioned, band zero).
The SM200A would be our recommended receiver if you needed better performance in this regard.
Thank you for your patience Jonathan. It was nice talking to you. Let us know if you have follow up questions/comments.
Regards,
Andrew