I have an OCZ Silencer 750 Crossfire (ESP12V) model, released in the 3rd quarter of 2007.
Is this PSU cabable or compatible power/connect to a AMD Radeon HD 7850, and new intel X79 mobos?
You should be fine (for now). Keep in mind that over time all PSU's lose some of their original capacity (eg. a 750 watt will really be on par with a 600 watt). The better built units degrade less (or slower if you will) over a longer period. This is why we all preach to get a good name brand PSU for your build. I've got a couple Antec's in continuous service for 10 years. Nothing critical or demanding mind you - mainly office type tasks. You're lucky. You got one of the better ones for it's time. I don't know if I'd push it with a cfx setup - but then again you might be ok. I won't suggest that you run right out and by a new one - but if you start setting a couple of bucks aside for the inevitable I wouldn't complain either.
I have one of those PC Power & Cooling Silencer 750 Quad's. Purchased it back in 2007 and it died three years later. I wasn't even drawing any more than 275 Watts from it. I had it RMA'ed under warranty.
For a system using a single Radeon HD 7850 graphics card AMD specifies a minimum of a 500 Watt or greater power supply. The power supply should also have a combined +12 Volt continuous current rating of 24 Amps or greater and have at least one 6-pin PCI Express supplementary power connector.
For a system using two Radeon HD 7850 graphics cards in 2-way CrossFireX mode AMD specifies a minimum of an 600 Watt or greater power supply. The power supply should also have a combined +12 Volt continuous current rating of 32 Amps or greater and have at least two 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 factor.
The PC Power & Cooling Silencer 750 Quad (S75Q), with its combined +12 Volt continuous current rating of 60 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 a single Radeon HD 7850 or even two Radeon HD 7850 graphics cards in 2-way CrossFireX mode.