Relation between speed control Bandwidth and encoder system

Dear,

As mentioned in the support for Sinamics products, Closed-loop speed control bandwidth is dependant of the type of encoder installed in the motor.

"In this case, the dynamic response is determined primarily by the encoder system."

For maximazing bandwitdth, what type of encoder/resolver is more appropriate to achieve the higher bandwidth ?

For harsh environment application, we would prefer resolver. Does this lead to some limitations regarding performances mentionned by the support (250Hz speed control bandwidth).

Thanks,