http://www.guru3d.com/articles-pages/radeon-r9-290-crossfire-review-benchmarks,4.html
According to the above review your PSU meets the minimum required for that Graphics Card. To be absolutely safe, and to allow further upgradeability in your system, you may want to consider a 700w or higher PSU but you certainly shouldn't experience power outages or hardware throttling with your 600w unit - assuming you don't have many, many hard drives or a massive string of 20+ USB devices attached to your system.