@ misd-again
I haven't seen LRC to be anywhere near .825. My understanding is that LRC equals CI 140 which is about M.84. Company settings may influence this though I have difficulty seeing how. This is not initial buffer margin... We all fly the same wing. ( I know, I know rake on the -300ER/-200LR/-F vs. the classic wing)
Regarding the speed range of M.815-.855, I fully agree.
Unless you have access to the FPPM or complex computer flight planning applications the only easy way to support is playing with the FMC. On the low speed side: put a HOLDat PPOS and note the airspeed that it provides ( it will always be a CAS) and convert that into Mach. At moderate weights it will seldom provide anything less than .8-.815 at altitude. This will be very close to your minimum drag speed. On the high speed end just put .855 and .87 into the CRZ page, the fuel deficit is quite significant. Again I'm assuming moderate weights, not 351.5 T nor a 175T ferry.
My 2 cents worth.