I understand obsessing over small parts.
Believe me, I tried every brand of rattle can out there.
Rustoleum was the worst.
Duplicolor was the best.
I ended up using duplicolor hi-temp for everything I was painting, as it provided the best results. The attached photo shows a part (the diff) done with duplicolor hi-temp.
The axle housing was powder coated.
A couple suggestions...
Clean the part WELL. Hi speed wire brush or beadblast. The paint needs something to "bite" to. Always prime first. Apply two coats of primer and two coats of color. First coat should be a light mist coat, second coat should be cover coat. I like Duplicolor self-etching primer. I let the primed part sit for 24 hours before topcoating. Apply your topcoats (start to finish) within one hour. Don't worry about a minor run. You can usually fix it with a third coat (yes, the run will blend and disappear). If for some reason after an hour you decide it needs more paint, you MUST wait seven days before applying more. Trust me on this one.
Finally, do not think a rattle can will ever match properly done powder coating....it won't. But you will get about 90% of the way there at a fraction of the cost.
Paul