I would go with a two stage urethane paint as the metallic in that color are very fine and like I mentioned in a previous post the metallics tend to move around a little when buffing and can cause a streaking or blotchy look. As far as durability between the single stage urethane and base clear urethane there may be a little more with two stage however I don't think it will be any factor on a classic car due to limited use. The UV rays from the sun are the most damaging to paint and most of the restored cars are kept in a garage with a cover on it, so I would not worry about durability. I painted my 70 BOSS 302 in 1990 with CENTARI enamel with a hardener which is not as durable as urethane and it shows no fading, of course the car doesn't get daily driven and it sits in the garage most of the time. Remember when painting a car most of your results are from the prep work underneath that make the paint look good and hold up. Use a quality etch primer over bare metal, use a two part urethane primer, invest in some good quality long, short and round sanding blocks, check your panel is straight by applying a guide coat, this is a contrasting color done with a spray can dusting over your build primer and when you sand this off when block sanding, any low spots will still have guide coat in them telling you more work is needed. After I sand down a panel I will also spray it with a paint cleaning solvent (water works too) and look down the panel and this will also show up any problems you may have before applying expensive paint. Sorry I got a little windy here but I can't stress enough about the importance of the prep work as it is like the foundation of a house. If a guy is doing prep work himself to save money these tips will save you a lot of grief. There are a lot of good videos and books available on this topic. P.S I have been doing body and paint work for 25 years