With GPU's gobbling power at unheard rates, it's important to choose your power supply carefully. You may save a few dollars on a bargain power supply but usually in the end, you pay more on the electric bill than you saved. It makes sense opt for a high quality, high performing power supply that might cost a few dollars more but shaves a few bucks off the electric bill each month. At low draw conditions, the OCZ Z 850W power supply hits about 81% efficiency but as load increases it becomes more efficient hittings as high as 91 - 92% efficiency. Let's say you are drawing 500W with that shiny new GPU setup but at idle you're hitting 200W. Your wall socket output at 200W should be in the 245W range (About 80% efficiency) but when you get into gaming, everything on your system kicks in consuming up to 500W. This is typical of GPU's like Nvidia's GF100, dual GPU setups, and dual core GPU's. The OCZ Z 80+ Gold Modular kicks up efficiency to 90+% so your wall sockets power output would be in the 550W range. Now take a typical 70% efficient PSU that costs a few bucks less, your wall socket output at 200W idle would be about 290W as opposed to the OCZ Z 850W's 245W usage which comes in at around 45W less. Now scale that up to 500W and the OCZ Z 850W's pull of 550W, at 80% (typical for 80+ Bronze PSU) and your looking at a wall socket output of 620W. The cheaper PSU with a 80+ Bronze rating is costing you more money every time you fire up your favorite game. Sure, the OCZ Z Series 850W Gold Modular PSU is costing you more upfront but not enough to detour a potential buyer, especially when the monthly return in savings makes up for the initial cost. Think about a 6 hour gaming session, 4 times a week at 70W an hour. That's 70x6x4 or 1680W per week, 1680x52 (a years use) is 87,360W or 87.36KW hours. Multiply that against your local KW hour rate and you have the hidden cost of less efficient PSU.Now here's the crux of the matter, less efficient PSU's usually aren't built as well. Lower quality PSU's can leave you open to PSU failure which can potentially take the whole rig with it when it pops. Spend the extra money for a good quality PSU like the OCZ Z Series 850W Gold and sleep well at night knowing your gaming shrine is in good hands.