Corsair HX Series CMPSU-620HX or 520HX PSU

I am looking to replace my Antec Neo Power 480 with either the Corsair HX Series CMPSU-620HX or 520HX. I am not sure which to get. The PSU also has to help exhaust the hot air out of my Lian-Li case. I used the tool to calculate watts and it recommeded 500w psu if I overclock. Should I go for the 520 or the 620 or is there another you would recommend?. I will be upgrading my mobo and CPU in the future. Motherboard will be the Asus P5 WDH deluxe CPU a Core 2 Duo E6400. You can look at my specs to see my setup. Thanks for any help!