PSU for overclocked 7970 - 150 MM in Length

Hi All,

I have begun purchasing the parts for this build

Planned Build -
CPU - Intel Core i5-3570K 3.4GHz Quad-Core Processor
Motherboard - ASRock Z77E-ITX
Memory - Samsung 8GB DDR3-1600
Storage – Samsung 840 Pro 128gb SSD
Storage - Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive
Video Card – AMD HD 7970
Case - BitFenix Prodigy (Black) Mini ITX Tower Case

The power supply I had in mind, microcenter didn't have. Thus I am looking for a new one that can power an overclocked 7970 and is 150 mm or less in length, due to my case.

Now, I had the SeaSonic M12II 620 Bronze 620W ATX12V V2.3 in mind, since it confirms to the length. Will I have issues with this. I tried that suggested online program to figure out the appropriate power and this seems to be ok, but I would rather have a second set of eyes before I pull the trigger on this.

Thanks.

-Dan