TX750 M or GS700?

Corsair TX750M will do excellent. I have been using the non modular version and its stellar. Corsair is a good brand Also the TX Enthusiast is a better built than their buy on the fly Gaming series
 
For a system using two GeForce GTX 260 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 650 Watt or greater power supply that has a combined +12 Volt continuous current rating of 52 Amps or greater and that has at least four 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important.

The Corsair Gaming Series GS700 (CMPSU-700G), with its combined +12 Volt continuous current rating of 56 Amps and with two (6+2)-pin PCI Express supplementary power connectors, is electrically sufficient to power your system configuration with two GeForce 260 in 2-way SLI mode but is deficient by two 6-pin PCI Express supplementary power connectors.

The Corsair Enthusiast Series Modular TX750M (CMPSU-750TXM), with its combined +12 Volt continuous current rating of 62 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with two GeForce 260 in 2-way SLI mode.
 



I am looking to updrage my graphics card in a while, thats why I would go for the 750W

Cheers for the analysis though :)