I decided to go with the Sea Sonic X-650 v2. It there a better model for that kind of money?
I mean you can get better and better but it's bordering the limit I want to spend on a PSU.
For me the question came down to how much power do I expect to pull off this thing in the future. So if your current PSU is doing fine and anything you might upgrade won't extend the limits of the PSU, no need to spend any money.
If however you'll be putting in parts that will stress it too much I'd say upgrade to the very next level. Antec is also a solution, they make excellent PSU and are generally more affordable. I got the X-Series 1050watt (coming from a 1000watt Antec) because I plan to Tri-SLI my Titan setup at some point and I'll need that extra juice.
But it's really just a question of get what you might need to future proof.