GPU - CPU Performance comparison on string conversion i7 860 3.5GHz beat out NVidia 9800 GT

Looking at the code, it really isn’t very suprising that the GPU is slower. The memory access patterns are about as suboptimal as you could possibly make them for a compute 1.1 device. There is a section in the programming guide which discusses the concept of memory coalescing and how to achieve peak memory throughput on the GPU. You might want to review it.