10tacle :
Buying a gold 600W PSU when my rig uses 500W for example does not make much sense to me. I'd prefer to spend a little more and buy a gold 850W ($110USD vs. $130USD in the example of these two 650 & 850 G3 series on NewEgg [US] right now). Not only for a higher efficiency operation as described above, but for future headroom growth. But I understand many do not think that and look to save a few dollars everywhere...one being on the PSU.
I see this logic around a bit and I have to respectfully disagree. The problem with making an efficiency argument based on max load of the system is that unless you have a relatively unusual workload (like bitcoin mining with 3 GPUs, for example) your system very rarely actually hits those peak levels of power draw. Very few rendering/productivity tasks fully load up a GPU, and gaming workloads don't fully light up the CPU - and when they do you're probably bottlenecking the GPU anyway.
Let's say a hypothetical build hits 500W when you fire up Intel burn test and furmark simultaneously while running a low-level disk check on all your HDDs, It's likely that same build sits at a much lower 300-350W in most normal gaming workloads. Obviously you want to be sure you can handle those peak workloads so a 550W (or, for some extra headroom) a 600W PSU is mandatory. But you should IMHO make your efficiency decision based on the most common load scenario the system will be sitting at. And 300-350W is right in the efficiency sweet spot for a 600W PSU.
Obviously you don't want to skimp on your PSU, there's no question about that, but I feel like I see many inexperienced builders on the forums here getting talked into spending big dollars on premium 650 & 750W units for their single GPU builds "just to be on the safe-side" when something like a CX450M for ~$50 would suit them perfectly.
