No upgrade needed. Your system with everything overclocked will not draw more than 375W. You have a good PSU so you don't need to be concerned with overload like you would a low quality PSU. Keep what you have until you're ready to go to X-Fire, you won't hurt anything power wise by overclocking your system as is.
Hope it helps
Edit: Note that AMD does not specify whether the system is overclocked or not - doesn't matter as far as their recommendation