>I don't have much experience with Sigma glass. Would you rate >it equal with top named brand lenses?
No way, not as a whole. But their recent releases have gotten gushing praise at about 60% of the price of Nikon equivalents. Read reviews of the Sigma 35mm f/1.4, most place it on par with or almost as good as the Nikkor 35mm f/1.4, and most reviews of the 85mm f/1.4 place it on par with or slightly better than the Nikkor 85mm f/1.4. Every lens including Nikkor lenses should be thoroughly researched before buying.
That said, a mediocre lens in the right hands will produce far better photos than a superb lens in the wrong hands. And as much as people make of corner to corner sharpness and bokeh, that's not what makes a great photo.