The CX series uses cheap capacitors and has longevity issues and while its not even close to being one of the worst units available it's not one I would suggest buying. The AX is a top tier PSU quality wise. It will run cooler, quieter, and last longer, but usually costs more. As far as power savings it more efficient so it will cost a bit less to run, but I can't really put a dollar amount on how much you'd save. Higher quality psus offer more stable power which can increase the life of other components and a can help with overclocking.