Well.. Acrylic is a paint that likes to expand and shrink through weather conditions.. ie heat and cold..
If you spray 2pak over acrylic it will crack.. 2pak dries hard, So if you have an undercoat that's expanding and shrinking under a solid hard coat of paint..
2pak shits all over acrylic/ enamel. I sprayed mine acrylic due to the fact it's easy to spray and easy to buff.. That's it. Now my cars getting sprayed at an actual paint shop i wouldn't touch anything other than 2pak..
After speaking to a spray painter of 40 years who said 2pak is the only way to do it properly.. I'll take his word
If you're after a nice grey colour look at the new commodores on the Holden site, There's a grey they've brought out now that's awesome, Gets almost a bronze tinge in the sunlight