A friend did a more testing, and ETH+LBC in R9 380 is a lot worse then ETH+ SIA
his rig stats are:
4x380
ETH/LBC = 70/55MHS
ETH/SIA = 85/900MHS
Looks like LBC is way to GPU intensive for R9 380 and maybe other card, impact on ETH is just to huge to have any benefit mining LBC and losing on ETH side more
Depends on Sia and Lbry price. For me it is a bit more profitable to dual Lbry, but there are recent crazy price jumps for both coins. Also dual mining LBRY takes ~15-20w less power per 470/480.