Well you won't regret it anyway, it should see through for a long time.
If you bought the system you posted on page 1, 650W should get you over the line, but only just. I'd say an 850W would be a better option.
You did remember to plug in the two molex connectors right?
http://www.guru3d.com/article/zotac-geforce-gtx-480/9