For that Rig, 850 Watts Psu is enough anyday.. even if you go for a higher perfomance gpus and couple of more hdds..
PS- the gpu makers if u notice are going green by lower the power consumption of their products these days.. so Any goo 850 watt psu wld serve your purpose.
I recently bought the Corsair AX850. If u can buy that then thats the best u can get among the 850 watt psu category imo.
A 750W or a 850W PSU would be overkill for your setup, a single GTX 560ti draws 170W at full load, 190W when overclocked heavily. A second card in SLI will draw the same totaling 380W, leaving around 2250W for the other components including overclocking so all you need is a 620-650W PSU.
The TX650V2 would be sufficient for your rig, as long as you're not planning to overclock your GPU.
The TX650V2 with 53A on its +12v rail is capable of powering your system with two GTX 560 Ti. Since that PSU has only two 6+2 pin PCIe connectors you'll have to use the two dual 4-pin Molex to 6 pin PCIe connector which are usually included with the GPU.