I'd previously noticed that a family member's Roku Ultra clocked its CPU between 216 MHz (at 850 mV) up to 1.5 GHz (at 1040 mV).
But the last time I was briefly there, his Ultra only clocked down to 700 MHz (at 850 mV). Did a firmware update raise the baseline speed, or did I not spend enough time monitoring?
P.S. FWIW his Streaming Stick+ CPU was capped between 216 MHz - 1 GHz (850 - 900 mV) but was still running hotter by 30-40 degrees F! In contrast the 2017 TCL Roku TV's stayed steady at 1.2 GHz (1000 mV). See here.