[rbanffy]

> They're specifically built GFlop and memory-bandwidth machines

That would indicate their theoretical peak performance is higher. Unless you can line up your data so that the GPU will be processing it all the time in all its compute units without any memory latency, you won't get the theoretical peak. In those cases, it's perfectly possible a beefy CPU will be able to out-supercompute a GPU-based machine. It's just that some problems are more amenable to some architectures.