Just found Griffon’s Eye, but sadly it is -15 resistance with perfect +15 damage 196 def, feels like I got trolled 
Is there a noticeable difference in damage between -15 and the average roll of -17 or -18 for light sorc for PVM ?
I’d say its somewhat noticeable. The difference between a min roll and a max roll for my current gearset would be about a 10% difference in average dps, on mobs that are having their immunity broken by Infinity.