On my very small samples (2 OSB, 3 OSB x Saddleback, 2 LBs) I can't say I noticed any difference in rooting between OSB, Saddleback x OSB and Large Black. Mind, mine always
need to root, they don't get given ground good enough to just graze!
Temperament of the LBs was quieter than OSB or Saddleback x OSB. Nice enough pigs, but didn't get under our skin the way the more flamboyant OSB and OSB xes did.
Growth rates were a lot slower than either OSB or Saddleback x OSB, so if you fed expecting those growth rates then I guess they would get overfat, yes. Conformation was also not as good as either OSB or OSB or Saddleback.
BUT... when the meat came back we forgave them the extra months and the poorer conformation. Just
delicious.

I would / will have them again. For the taste and
because they don't get under your skin the same way the OSBs do
