Basically, I'm looking to update my Geforce GTS 250 to a DirextX11 capable card.. probably a Gigabyte GTX 670 OC card. From everything I've been reading, my PSU has 4 12V rails at 18A, 18A, 30A, and 30A for a combined 62A at 744W. Again, from my reading and someone please correct me if I'm wrong, but the PSU should be able to handle a single overclocked GTX 670 just fine.
What about SLI if I decide to go that route in the near future? A PSU upgrade would probably not be out of the question but I like to plan ahead and also double check that I'm correct in that my current PSU will be able to handle 1 of these cards, if not 2?
I agree that the wattage is probably fine.. I'm more concerned about the amps on the 12V rails. I agree that for one of these cards it should be fine, I'm just not sure about two.
They don't exactly make it revealing as far as which cables share which rails. It has two 6 pin and two 8 pin cables built in plus whatever modular cables (I'm pretty sure there are a few 6 pin modular cables but I'd have to check if there are any 8 pin ones for PCI Express cards).
For a system using two reference clocked GeForce GTX 670 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 700 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 45 Amps or greater and that has at least four 6-pin PCI Express supplementary power connectors. The Gigabyte GeForce GTX 670 OC WindForce 3X 2 GB GDDR5 requires one 6-pin and one 8-pin PCIe power connectors for each card.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most important factor.
Overclocking of the CPU and/or GPU(s) will require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock being attempted.
The Thermaltake Toughpower 850W (W0178RU), with its maximum combined +12 Volt continuous current rating of 62 Amps and with two 6-pin and two (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with two GeForce GTX 670 graphics cards in 2-way SLI mode.
You have at least 17 Amps of spare capacity on the +12V rails to handle any overclocking of the CPU and/or GPUs.
You should be able to determine if each of the hardwired 8-pin PCI-E cables are on a separate +12V rail by looking at the color stripe on the yellow +12V wires for each of those PCI-E cables.