Lots of good advice here!
I'm no expert, but i've known a few. I think my best advice would be to pick a painter (by looking at examples of their previous work) and let them choose the paint. Ask a painter to use a paint that they're not familiar/comfortable with, and you'll end up with lousy results no matter how "good" the paint is.

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I agree with most of what tedro 951 said. Adding to that;
Porsche and Ferrari used glasurit 21 line (single stage) paint for solid colors and 54 line (basecoat/clearcoat) for metallics during the '80's and '90's. Glasurit came out with the 22 line for single stage and 55 line for solid and metallic colors in the late '90's. So if your car has original paint it is a glasirit single stage.
I have used alot of different brands and have settled on glasurit. I used 7500 and the nason clears and was unhappy with the look, but not because of defect. I'm not sure how to describe it, for lack of a better word, it looked cheap, fake. It would look fine on a domestic car but didn't have the refined look of the original paint.
I don't agree that having a painter use a product they aren't use to using will produce a lousy job. I've sprayed alot of different materials and never needed to practice with them first. There are differences in viscosity, pressure used, etc. But a good painter can work these out without much trouble. Setup changes but not technique.
The most important thing to do is know how spot defects and then to look at the shops work. Most people don't notice small imperfections until a trained eye points them out.
Compare paints (on the cars) side by side if possible, you'll see the difference.
I think a single stage glasurit looks just as good if not better than a Dupont/nason BC/CC. I posted pictures awhile back in the 928 section to show as a comparison.
Do your research on products and the shop doing the work. Its not just what the car looks like when it comes out of the Booth, its what it looks like a month (or more) later when its fully cured. Solvents evaporate, filler/primer/paint shrink and then sand scratches show up on a hastily done job.

another thread back from the dead.....:)