I have done a few spray outs recently for Corvettes and sent them in to the NCRS paint guru's, the most accurate metallic sprayouts were done as follows.
Scanned the color in the dealer album - and then reduce the metallic content that the camera reads by about 20% - in addition add 20% flattener in order to knock the Urethane look off of catalyzed paint.
The way you shoot it will alter the color, most of the guys painting NCRS Corvettes are also shooting one coat of pure base, 2 coats of 50% base 50% clear with a wide open fan pattern, then one coat of clear. This will get you very close to a lacquer look.