most of the gpu algos out there are memory bound, so increasing your core voltage and pushing the frequency of the core higher = just burning more electricity and creating more heat over actual work.

your best bet is to push the memory as hard as possible, reflash bios to reduce memory timings as tight as possible. undervolt the gpu core to generally around -20% power limit, and push gpu core as high as possible while still maintaining stability.

Anything else? :D