according to http://www.eggxpert.com/forums/thread/323050.aspx
StealthXStreams from before December 2007 Are not great.
In general OCZ PSU's manufactured before this are not very good.
With powersupplies it is always a matter of risk. In most cases even really cheap ones perform fine as long as you dont go beyond 70-85% of its rating. But the cheaper/worse it is, the bigger the risk it will suddenly go poof. And there is always a risk it takes something with it.
There is also a chance it will cause other components to wear out faster, not to mention make it harder to overclock things.
In short, you choose how much money you spend on your power supply, 700W should be enough for that GPU, even with some room to spare.