I'd go with auto paint too... Auto paint has some "Gloss" to it, In the old days it was Enamel or lacquer, not it's mostly acrylics. but it's a much harder finish than latex, which is after all rubber, and what's more when properly applied and rubbed out it is a very very very smooth paint (you can't rub out latex far as I know)
What does "Smooth" mean to you.. Why MILES PER GALLON of course cause the slicker the paint job, less "Drag" from the air you are driving through.
I've seen a car pick up 20% MPG from a wax job
I know.. I applied the wax myself.. Simonize, the old fashion kind.
Home is where I park it!