Claymore is MEGA-monster! 
RX480 4G with mod. mem timings = 70-72 sol\sec
RX480 4G with mod. mem timings = 70-72 sol\sec
wich timings are you using?
can you share the rom?
thanks
ROM (from MSI RX480 4G, only for HYNIX memory):
http://hushome.com/img/patched2(1950stable).rom (click rmouse and select "save link as...")
Overclocked memory from 1750 to 1950@1000mV (or 2000-2050@1250mV - this may damage your card)
Result:
