Seriously, I think the Corsair TX 650 Watt Modular is perfect for your setup.
The TDPs are:
FX8120 = 125 Watts
2 x GTX 560ti = 340 Watts
Given your SLi setup, the total max wattage for the system would 465 Watts + other devices. The Total overall at max would probably be around 500 Watts (including motherboard chipset, drives, ram etc.).
Now this is the maximum. Remember, the TDP does not necissarely equal the power draw. The TDP is the maximum amount of heat to be dissipated by a cooling apparatus. So your system would only consume about realistically 450 Watts DC at maximum. You would only reach the maximum amount of power consumption if all of your hardware got insanely hot because of the increased resistance caused by high heat.
Now the bulk of your power hungry hardware will consume power on the +12V rail, including GPUs and CPU. Looking at the chart for this PSU:
http://www.corsair.com/power-supply-units/enthusiast-series-power-supply-units/enthusiast-series-tx650-v2-80-plus-bronze-certified-650-watt-high-performance-power-supply.html
you can see that the PSU can deliver 53 Amps of current on the +12 V rail, giving you 636 Watts maximum, well above the 450 Watts or so that you would realistically be drawing from the +12 V rail.
So my point is that it would be false to say this PSU would be cutting it close. This is where I think Guru3d is totally off the mark. It was even shown in the article that the system wattage with gpus in full stress was 449 Watts AC from the wall. Factoring in the efficiency of the PSU, I would say the system was consuming no more than 400 Watts DC from the PSU. Now guru3d may be taking into account the fact that not everyone has a quality PSU and these PSUs often dont have the 12V rail wattage proportion that the higher end ones do like corsair (My first PSU was a 650 Watt but only had 456 Watts on the +12V rail). I would however say that if you want headroom for future upgrades, you should consider a power supply with a larger capacity.
Other than that, this PSU would do the job very nicely, with still a fair bit of headroom. Now if you overclock the GPUs and CPU, the system will consume significantly more power but your system will most likely still be consuming power safely within the limits of the PSU's wattage capacity.
I say go for the Corsair V2 TX650 M. You have nothing to be worried about. Going any higher than 650 W would be serious overkill. Heck you could probably run it nicely with a TX550M.