Picking the right PSU

[PowerOfFailing]

Hi! So, I've been having a lot of problems with my GPU lately (GPU high load -> system shuts down without any error messages) and I am getting tired of it. I know that the GPU itself is not the issue here, so I think it is the PSU's fault. Currently, I own a Corsair VS650 650W PSU, which feeds a GTX 970 and a Core i5 2400. Recently, I have been trying to decide what PSU would be good. I know that under load, my system doesn't pull more than 300W from the wall, so I guess I should be looking at the 500W-600W PSU category. Right now, I am deciding whether to pick:

Seasonic M12II-620 Evo
Seasonic M12II-520 Evo Edition 80+ Bronze
Seasonic S12II-520
Seasonic S12II-620

What do you guys think? Or, does anyone have a better suggestion for what PSU I should get?
Thanks!

 

[BadActor]

The 520 would have enough wattage. S is non modular, M is modular. I have the S12II 520 running a GTX 770 with no issues. Good quality for the price. Another one to look at and might be slightly cheaper is the XFX TS 550.

http://www.realhardtechx.com/index_archivos/Page362.htm

http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html