great power supply and yeah that deal was for the x750 for $90 after rebate. the cheapest the x850 has been was $120
Ah ok cool, I stand corrected. BTW - makes sure you check Seasonic's power efficiency charts on their website for the model you are looking at. It's very useful information to have when choosing a PSU size. My original thought was just get the biggest and best, BUT, if your PC is only drawing say 20W on idle and 300W at load, an 850W PSU will not be as energy efficient as a 650W PSU. What you want to aim for (and you need to check the chart for the specific model), is for your load to be in the 40-60% range of your PSU for best energy cost savings and heat & noise ratios. You also need to consider how ofter you'll be at load on any given day to get a feel for it.
Use this website to see what your wattage will be, and basically double it if you're going to use a Seasonic PSU. They are great PSUs. Remember to switch the device to hybrid mode to turn off the fan when not needed.