bytemaster still hasn't responded further to my logic that the GPU can mine much faster (specifically he hasn't stated why he believes a hash table can't also be implemented on the GPU). He said he is sick.
GPU's will be able to generate the SHA512 hashes quicker, no doubt. But the GPU resistance relies on the GPU not being able to store them. So if your GPU is generating 10GB/s but can only store 1GB/s, there's no advantage to an i7 that generates 1GB/s and stores 1GB/s. Whether that's through the medium of a hashmap or not is not important.
ByteMaster really wants to know if there is a way to beat this with GPU's - that's why he's put up the bounty.