Always fun to upgrade. If I was you I'd just keep using that Corsair HX620, it's a rebadged Seasonic and they make kickass PSUs. OCZ bought PC Power and Cooling but never seemed to do anything with them, they've been rebadging cheap Sirtec and ED Group PSUs for eons. OCZ in general is kind of a dodgy company, they were caught using cheap grade NAND awhile ago and their Sandforce SSDs were nothing short of nightmare.
Have fun with the build, I love putting together a new machine.
Playing: Dark Souls 2: Scholars of the First Sin Watching: Mr. Robot