Maximum rotation rate for digital compass
The sampling rates available on magnetometers such as the HMC5843 do not come anywhere close to the bandwidth of the underlying anisotropic magnetoresistive element. For proof, we can look at the datasheet for the HMC1001, an analog AMR magnetometer, also from Honeywell. The datasheet states that the bandwidth is from DC to 5 MHz typical. With the 116 Hz sampling rate of your magnetometer, you're not going to be able to detect any bandwidth limitation of the sensor itself.

Incidentally, the HMC5843 is obsolete. You'd be better off with something like the HMC5983 (which is technically obsolete, but widely available) or the MMC5883MA.