I understand you folks don't know me, and maybe don't trust me as much. But in this case, I'm right. In that Guru3D article, with the GPU at full stress, their system was pulling 312W from the wall. That means after losses from the power supply. We don't know how efficient their power supply was, but probably in the 80-85% range. That means that running Furmark the system was pulling, at most, 250-275W. With that type of load, it doesn't really matter what his CPU is, anything short of a very overclocked 980X would be safe, especially since it's unlikely he'll be running Furmark and LinX at the same time all day.
The 6950 is at the "break point" between 400W and 450W for me. If it makes you feel better I can recommend a 450W instead. But I'd bet cash money that if he chooses a quality 400W power supply (Antec NeoECO 400C, Antec Earthwats EA430D, SeaSonic S12II 430W, OCZ StealthXStream 400W, OCZ StealthXtream II 400W, Rosewill RG-430, etc.) he'd see no power-related issues at all.