The thing is that power supplies don't have constant efficiency; they're usually most efficient at 50% load and tend to drop off above/below that, and are especially inefficient at low loads. Your computer would never use more than a third of what your PSU can deliver, even at 100% load with everything overclocked. When playing games you wouldn't use more than 300-350 watts, and when just doing normal web browsing the power usage would be around 100. I'm not saying it's wrong to use a 1200W PSU, I'm just saying it's not optimal.
Oh and the GPU Nvidia's been recieving flack over is the 970, but IMO it's not worth worrying about. The problem is that only 3.5 GB of the 4 GB of VRAM are usable; the last 512 MB are still accessible, but run much slower. It's not really a big deal though, and the cards are still superior to AMD's offerings.