George...It is my understanding, for derating purposes the 90C column is used.A 8-3 romex cable run by itself needs no derating.
I interpet the MA code (334.80) that I posted to mean if the 8-3 copper romex I run in a dwelling is imbeded in thermal insulation that I must use the 60C column which restricts the wire to 40amps.
If the wire is run through the basement(which most houses in New England have)along the sill and up through the floor to the freestanding range, NOT imbeded in thermal insulation, then the wire will be good for 50 amps as listed in the 75C column in 310.16
Also take note of the temperature correction factor table below 310.16. If the wire is run in the basement where the average tempature will be 70F-77F or lower around here, I can apply a correction factor of 1.05...or 50amps x 1.05= 52.5amps
On the other hand if the wire is run up through the ceiling embeded in thermal insulation exposed to attic tempatures in excess of (lets say) 114F-122F, then I would figure the amperage of that #8 copper romex from the 60C column with a tempature correction factor of .58...40amps x .58= 23.2 amps.
Quite a swing in allowable ampacity
shortcircuit