The Soviets did not have the technology to make blades that could tolerate as high temperatures as the J58 turbine. As a result, the MiG-25 Foxbat flew slower than the SR-71 Blackbird. //

‘As it turns out, the Soviets did not have the technology to make blades that could tolerate as high temperatures as the J58 turbine. As a result, the MiG-25 flew slower than the SR-71 (Mach 2.83 rather than Mach 3.4), and its engine did not last the 400 hours between overhauls that the J58 managed.’

In fact, the SR-71 and MiG-25 are both thermally rather than power limited. Both have reserve power to climb (rapidly) at full speed. Their speed is limited by the temperature of their turbines, and not by power.