not sure I'd trust that 500W power supply. I'd feel better with maybe a 600-650W range. Gives you a little wiggle room for future expansion. Since you are going with the 80+ certified design... that thing should last you a loooong time. So it would be worth the investment now while you can bundle it with the system.

Not sure how your power grid is, but you may want to look into a UPS also if it's in your budget to protect your investment. Something in the 1000 VA range should give you a nice window for getting to a safe area to log out of the game and shut down (with a monitor and network hardware on it, you'll probably draw 450W+ on it). An 850 technically should work, but it would drain it enough to maybe only work once or twice before the battery is drained if you are having a lot of interruptions during a bad storm (like we just had come through the south east).