I have clear examples of limits that not only stand but enjoy: Motorhead, Venom, Goddess Of Desire, Coroner, Sabaton, Abandoned, Exorcist, Celtic Frost, .
Grave Digger, Dark Angel, Kreator and Sodom are on my extreme border and I only stand a few albums.
I listended to Cannibal Corpse along five albums until one day I grew bored totally of being unable to distinguish one song from another and can't sing along so I got rid of them all.
I dug an ocassional growl in early Lacuna Coil albums, in some Ayreon albums, in Beholder albums, even in a couple of Nightwish songs (but not in "Once", Marco IMO exagerated his vocals because in Tarot he sings very neat).
But as examples Mercenary and Epica bust my b... out completely at PPVII, I could skip the first but had to endure it the second to keep the seats for Jorn (but Pabla stood watch with me so she also deserves a commendation

). Have to remember to carry a walkman next time just in case
