You can select different Power modes for RX and TX on the GTX page of XPE 12.1.
The two choices are Low Power and High Perf.
Low power should be selected when GTX runs are less than 3.25Gpbs
High Perf should be selected for runs above 3.25Gbps.
Both modes are selectable even if the data rate is less than 3.25Gbps, and the tool gives different power results.
Both low power and high perf mode are selectable even when the data rate is less than 3.25Gbps because VCO can be run at low and high frequency for the same data rate.
Low Power mode deals with low frequency of the VCO, while using higher VCO frequency gives higher jitter performance which relates to high perf mode.
These settings are available in XPE only and there are no plans to document this settings.
You can use these settings to estimate the power advantage gained by using VCO at lower frequency.