Originally Posted by pez
Since you admit upgrading the CPU might cause some bad turmoil between the parts in your PC, a PSU upgrade should just be the next choice. My current PC under load draws around 515W with the GPU at stock and I believe around 530-550 with it OC'ed.
You don't have to go overkill with the PSU (like I have done), but just look for a good 600-650W unit.
Not sure how yours draws so much...
Mine peaks at around 350W at the plug (so actual used will be something like 80% of this), and that's running FurMark. Running something like IBT as well pushed it up to nearer 400W, but again that's at the socket. And this was with my 920 at 4.2GHz.
I think he'll be fine with an overclocked X4 and a 5870.. I think most people go overkill on their PSUs, generally there is more headroom than people think. Obviously this isn't true of bad quality PSUs, but I don't think BeQuiet PSUs are especially bad.. in any case, I think he'll be fine running what he's planning to