Which PSU and how many Watts?

Hey, so far i have the following:

CPU: Intel i5-3570k

Cooler: Coolermaster Hyper 212 EVO

GPU: HIS HD 7950

Mobo: Asrock Z77 Extreme 4

RAM: 8Gb G.Skill Ares 1600MHz (2x4Gb)

HDD: Seagate Barracuda 1Tb

DVD: Samsung 22x DVD-RW

Case: BitFenix Raider


Currently looking at these PSU's,

Silverstone Strider Plus 600w,
http://www.pccasegear.com/index.php?main_page=product_i...

Antec TruePower 650w,
http://www.pccasegear.com/index.php?main_page=product_i...

Antec High Current Gamer 620w (modular version),
http://www.pccasegear.com/index.php?main_page=product_i...

Seasonic S12II 620w, (i know its not modular, but if it's really good then...)
http://www.pccasegear.com/index.php?main_page=product_i...

Suggestions from this site plz thankyou:

http://www.pccasegear.com/index.php?main_page=index&cPa...


Other info: Looking to overclock GPU and Cpu (not massive overclocks). Might Go Crossfire in the future with another 7950. Would prefer Modular/semi-modular.