Thanks mate,
I used the ref RX480 LN2 BIOS which worked fine. and used elmor's eVc for voltage.... I didn't check if gpu tweak it worked its possible it would have.
card ran fine at 1760 core and was still showing signs of going further... but I ran out of LN2.
also be a where that I had a hot burning smell at high volts .... which is why I had the slim pot over the vrm area.... (not sure if it was vrm or chokes) but it helped.
good luck!