To be honest, my Uncle has 2 common plecos in his Oscar tank and they seem to co-exist without any problem i.e. no pieces missing, no apparent stress, proper growth. You should always research it of course, but there are always exceptions to the rule and unfortunately, it's a case of trial and error.
My Gold Gourami is supposed to be an aggressive bully when he's probably the most mellow fish I've owned aside from my catfish.