Choosing sampling rate according to the bandwith reponse in accelerometer datasheet
See the relevant notes on the data sheet:

5. Use an RC filter with 1.0 kΩ and 0.1 µF on the 
outputs of the accelerometer to minimize clock noise 
(from the switched capacitor filter circuit).

8. A/D sampling rate and any external power supply 
switching frequency should be selected such that 
they do not interfere with the internal accelerometer 
sampling frequency (11 kHz for the sampling 
frequency). This will prevent aliasing errors. 


Looks to me like the bandwidth numbers of 350 and 150 are the ones you should use.  The RC values they supply are at about 1.5 kHz.

There seems to be an switched cap filter clocked at 11 kHz that shapes your signals.  Also, the system depends on a resonance in the nano-elements in the 3-6 kHz range, but that doesn't mean that it can detect or report acceleration in that range.   

The 11 kHz signal, and maybe some of the resonance is going to bleed through, and that's why they want you to filter at 1.5 kHz.  That said, because they actually prefilter internally for you, you just need to cover the bandwidth of the accelerometer (at 350 and 150) with your sample rate.  800 Hz sampling should be fine!!