Hi Marcus,
Sorry for leaving the title empty, that's the first time to post to a mailing list. This is also the first time to reply, no sure if I replied correctly.
I use 390.625k as the sampling rate because this is the lowest I can get using the Ettus X310 without giving me a warning saying that the sampling rate cannot be provided by the hardware. The application is just transmitting a file using GMSK modulation on the two daughter boards of X310.