New psu

http://www.amd.com/us/products/desktop/graphics/ati-rad...

Your current PSU is fine since it is 600w. Also, I just switched from a Cooler Master to a Seasonic due to the fact it didn't meet it's listed rating. Most Cooler Master PSU's are over rated by 50-100w. So your PSU would still be the same wattage even if you did change to the 700w Cooler Master.

Don't upgrade the PSU unless you are going to run 2 graphics cards in Crossfire or your current PSU sucks. But 600w is good enough, and the manufacturer for the video card recommends only a 500w PSU. So if you have a normal system, not too many expansion cards or more than 3 hard drives, I wouldn't worry about it.

I would definitely recommend an upgrade the X-Silent has an unstable 12v rail and no 8pin mobo power lead.
If you ever go to a different mobo(most require 8pin)you're SOL with the X-Silence.
An unstable 12v rail is scary!it's the most important rail that supplies power to your system components.
A quality 650W unit will run 2x5850.
XFX P1-650X-NLG9 XXX 650W Modular Power Supply -£71.96 Inc VAT
http://www.scan.co.uk/products/650w-xfx-xxx-edition-mod...
Antec True Power New 650W Modular -£69.56 Inc VAT
http://www.scan.co.uk/products/650w-antec-truepower-new...