I'm too lazy right now to read too much about those, but Bryan may be the one to ask. He's got some old server processors running some of his beastly cards, and may be able to provide some insight...

Are you implying that the bottleneck would occur with the CPU trying to feed the GPU? If so, Bryan's solution was to leave the CPU idle, only using it to feed the GPU. Compared to the GPU, that you wouldn't miss the CPU credits...