Well, the 7870 uses a max of 160ishW~14a on any given day, and the 3570K has a 77W TDP, which of course increases with overclocking, but should not go over 110W or so. We'll say that the 3570K uses about 10a.
We'll go with like 26a total or so, and this is on the maximum load. The HCG620 can put out 48a of continuous power. The 520W NEO ECO has 40a on the 12V. It should be a sufficient amount of power to run the system even when overclocked.
I like Antec because they have alot of amps on the 12V.