I know OCZ is a good brand, so the 550 *should* work. At the same time, do you really want your PSU to be running full blast when you play games? probably not. I would just go with another quality brand PSU of about 650-700 w. That will be plenty to run any single graphics card out right now.
will work just fine for what you need and its half as expensive.
As for suggestions, I would just get a nice GTX 570 with a non-referenced cooler. a gtx580 is not worth it for an extra $120 for 10% increase and the equivalent radeon card to the gtx570 (HD 6970) is hard to find and generally more expensive for roughly the same performance. If, however, you are playing games at above 1080p resolution, I would go for the 6970. Otherwise, stick with the gtx 570.