Hi! I simple modded the timings (copied the 1500 in all higher) of my rx480s (msi, asus, xfx) and encreased my hashrate from 150 to 170mh with overclocking 
My shares fell down to one third. After i noticed, i disabled the oc the shares went up, but are still less than without OC and Mod.

Thought bios modding increases hashrate AND shares