Yep. I'm positive. Wattage is not as important as amperage. Lower end units add in minor rail amps to the total power of a unit while higher end brands like Seasonic label their units with 12v rail power only. Since the 12v rail powers the big stuff like the graphics card and CPU that is really all that matters when selecting a power supply.
The Seasonic G 550w unit provides a full 45 amps on the 12v rail and since amps ( 45 ) x volts ( 12 ) = watts you get 540 watts of the rated 550 watts on the all important 12v rail.
The Corsair CX 600 you have provides 46 amps or 552 watts on the 12v rail.
See how that can be misleading? The 550w Seasonic is actually only 1 amp or 12 watts less powerful than a unit rated 50 watts higher. Even more the Seasonic is rated to put out that power at a 50C ambient temperature while the Corsair is only rated at 30C. 30C is a hot summer day in many places much less in a hot computer. The Seasonic can also pull quite a bit more than it's rated at while many lower end units can't even meet their rated power ( the CX can, usually).
So quality and output aside a system with an R9 280 needs a recommended 550w power supply.
http://www.realhardtechx.com/index_archivos/Page362.htm
The 550w recommendation assumes you don't have a quality unit and leaves headroom for overclocking. Check here:
http://www.hardocp.com/article/2014/10/14/xfx_r9_280_double_dissipation_3gb_video_card_review/9#.VXH_D-LqE1I
As you can see the whole system with an overclocked XFX R9 280 Double Dissipation 3GB pulled 337 watts. That leaves you a very safe 200+ watt headroom at max draw.
Get the 550w unit for what you have now or the 650w unit if you plan on upgrading.