SUServo is, of course, a closed-loop system, so I was referring to the bandwidth at which the disturbance rejection reaches unit magnitude (i.e. noise is no longer suppressed). Below that, the disturbance rejection will improve as expected from the loop design (20 dB/decade in the low-frequency limit).
I'm not sure what you mean by "self-excited", but typically, you'll want both P gain and I gain. The appropriate gain settings strongly depend on the system parameters, but to give you a vague starting point, for a typical well-configured system, we might use P gain 0.5 and I gain 500 kHz.