Smartpowers aren't as reliable as they should, i would look for something else, i used to have one but decided to upgrade to a Corsair 520W for sanity, although it would be capable of powering your system if you already have it.
That's probably gonna be a little close, especially if you decide to go with something more powerful than the 8600. You can put your specs into this site: http://www.extreme.outervision.com/psucalculatorlite.jsp and it will give you a rough estimate of what your system will draw. Then allow at least about a 20% headroom.
It would be capable of providing enough power. It powered my hot x1800xt for a year, but i began to read numerous reports about smartpower 2.0s being unreliable, and from day one there was a noise coming from the psu because the power draw my x1800xt was putting on it so i just decided i didn't want to worry anymore.
Well the 8600gts is not good, it's between either the X1950pro or the 8800gts 320, if money isn't tight obviously the 8800GTS 320mb is the best choice. If you want more performance than a x1950pro but dont want to go to a 8800gts 320mb get a x1950xt 256mb, they should still be in stock.