I'm planning a build for sometime after the beginning of Septembet which will be based on the Haswell processor (most likely an extreme part). I want to include 3 graphics cards (will probably wait for AMD/Nvidia to move to the 8000 series/700 series) and would like to know if it's best to go with a dual PSU or one PSU with high wattage.
I'm planning on the new RoG Z87 motherboard's deluxe version, water-cooling with dual pumps, some lighting, 4 RAM modules, 3 GPUs (I'm thinking 89not90), an Asus sound card (probably a Xonar), and I will be overclocking everything. If I'm using current high-end parts instead, I think it would add up to needing somewhere around 1200W (this is off the top of my head) to run with, maybe, some margine to spare. I want to reuse my current case and a few other things including the radiator, but if I have to go for 2 PSUs then I will need a new rad and a modified plan.
You could go for a 1500W suppy for headroom with overclocking (if you're going to be messing with voltages and etc.) I've seen rigs running 4-way SLI with 1200W supplies. Also, assuming Nvidia and AMD continue with their current trend of reducing the power requirements for their cards, maybe you wont have to run that high on wattage. Silverstone and Thermaltake have some 1500W supplies, but I couldn't tell you much about them. I would personally recommend you go with a single supply to make things easier on yourself as a builder.
choose one u like from the list. all the selected brands are well known for their reliability. it turns out that they are all at least 80+ silver, although I didn't exclude bronze....
The concensus here is that I could do it at 1200W. I guess I will know for sure once the complete set of specs for the Radoen HD 8xxx and GTX 7xx are released as those will be the major sink for wattage.