I remember going through something similar. The Krylon Rust Tough Semi-Flat (which is good paint) is much flatter than Dupli-Color Semi Flat Black. If I recall, I would say the Krylon is about 40% gloss, the Duplicolor is 60%. I made the mistake once of spraying about 5 brackets with Dupli-Color, then one bracket with Krylon (after I ran two cans of Dupli-Color dry), and they didn't match.
So I wouldn't forget this in the future, I took a few thin sheets of aluminum and cut them into squares about 2" x 2", sprayed them with literally all of the various spray cans I have on my shelf, then taped each piece onto the appropriate cap. I got tired of always guessing the differences between flat, semi-flat, semi-gloss, and gloss between the manufacturers.
That's a GREAT idea! I'll look at the HD store to see how cheap I can find some plate. Not only that but a 2x2 swatch is easy to take to the car to check for samples.
I do think I have the rattle cans down for gloss, semi gloss and flat at the moment. Since this IS NOT a show car I have been trying to keep the car as close as possible to OE on a super low budget. These paints are not perfect but I have been checking around any other forums and these seem to be widely accepted.
As soon as I get some good samples and pictures I will post the colors.