Welcome to the forums, newcomer!
How old is the PSU you're working with now? Considering a PSU will degrade over time once you bring overclocking into the picture, meaning that the PSU is likely outputting far less than what the unit did while it was brand new.
Also, wait a little to see what the reviews have to say about the power draw of the card. Some people who fabricate cables/sleeving are already having a tough time figuring out the connector for the proprietary connector. In fact, it's not even made by Molex(the brand, not the 4pin plug).
There's also the matter of the card being just announced, you should wait to see reviews of the card before making a decision to buy it.