Could I run dual R9 280xs in this build?

[NocNautilus]

Also, would the performance increase be worth the money, and is CrossFire supported enough that this wouldn't just cause me infinite trouble and heartache?

Fractal Design Define R4
MSI 970A-G46 Motherboard
AMD FX-6300
Corsair H55
AMD R9 280x Gigabyte 3GB
Corsair CX600M PSU
2x4GB Corsair Vengeance DDR3
Samsung 840 EVO 120GB SSD
Qnix QX2710 27" 2560x1440 IPS Monitor

 

[ruecklm14]

Your cpu would bottleneck and I doubt your psu is big enough. I recommend at least a 750w psu.