A build such as this is estimated to draw just under 400w. The GPU won't draw anywhere near 300w; it's surprisingly energy efficient. A quality 520w PSU will be sufficient. You're more than welcome to hang around and gather more replies and opinions.
Just a thought... If you can afford a PS twice as big as you need, you will have the highest efficiency as most PS's are most efficient at 50% output. Not to mention it gives more room for future upgrades. I just switched from a Thermaltake 600w 80 plus ( 5 years old - worked fine, just needed one for a soon to be HTPC build ) to a Corsair AX750 Gold Plus and my power consumption on my system went down 34 watts according to my Cyberpower UPS.