GPUs are multiple orders of magnitude faster than a CPU's max theoretical throughput. If a GPU is slowing down the solution is a faster GPU, the CPU won't be able to help out much at the same stuff.
You think running on a CPU would save power? CPUs are the least power efficient because they are the most general. You should put some numbers on 'running slower' and 'less powerful'. GPUs for the same power are going to have about 20 times more single precision floating point operations.