Depends. Limbs have accelerated wood growth below to support loads,
which doesn't happen much with (vertically-oriented) trunk. So there
are structural differences, which may mean something. 20" diam.? 20"
Probably not a lot of research into this property of any pine, because
of its being kinda down on the list of fuelwoods. (We're fortunate here
with choice of excellent fuelwood species.)
IMHO, if it can't be split with a 6-lb maul, then a preparatory
chain-saw rip along intended split line should do it. Else, rip