MiG-25/MiG-31 versus SR-71 and the 20 fastest jets ever

I was reading the other day in another forum some quit interesting ideas but one looked quit impossible, i have read and know that the MiG-31 only can keep the Mach 2.83 speed for some few minutes but a person said that the SR-71 can keep it`s speed for several hours something it seems unlikely at least to what i know.
What i have read is the the SR-71 never was shoot down because once the MiG-31 was deployed simply all the violations of the Soviet/Russian air space either were so quick or the SR-71s always avoided the MiG-31s.

I doubted the SR-71 can fly supercruise at Mach 3.3 for hours while the Soviet MiG-25 can only keep that speed for few minutes, if it is true the SR-71 carries more fuel also is heavier than the MiG-25 and still the SR-71 is heavier than bigger Foxbat derivative, the already well know Super Foxbat or MiG-31.

Also some said that the Mach 4.5 AA-6 carried by the MiG-25/31 series would need a supercruise platform at Mach 2.8 to shoot down the SR-71 i hardly believe that an squadron of 20 MiG-25 or 10 MiG-31 can not hunt an intruder like the SR-71 unless the Russians had no interception time and the violation of Soviet/Russian air space was brief.