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that doesnt sound too far off. I'd say you can if you are not stressing the system with many other demanding devices. That PSU is good quality--thats why I'd say go for it.
nVidia recommends I think 550W for an SLI rig, but that's to cover the whole spectrum of available PSUs on the market because some are very crappy while others are very high quality. Yours is quality, so it can output more when the temps get going (production of a PSU goes down as the temperature of the PSU goes up, lower quality PSUs have higher performance degradation). You'll do fine, unless you have other power hungry components. Plus, you're not running two ultras.