The maximum frequency of a triplicated MicroBlaze subsystem itself is generally not significantly reduced. However, the majority-voted outputs from the subsystem impose an additional logic level, which might affect the overall frequency.
When using the internal SEM option with the TMR SEM core, the frequency is limited to the SEM sub-core maximum frequency. To avoid this limitation, the external SEM option can be used, to allow clocking the SEM with a slower clock.