Did I miss where on the vehicle this is going to be used?
IMHO, a satin or "semi-gloss" type finish is much preferred over straight flat or gloss black for underhood sheetmetal, firewall, accessories and brackets, etc.
On my Camaro underhood and A-arms, etc. I used enamel (Centari w/a flattener). IIRC GM is supposed to have used 60/40 in the muscle car years, but it looks a little too flat to me, we ended up about 75/25. This shot excellent- I'm a rank amateur and even I couldn't screw this up.
In looking around the interweb, SPI gets very high reviews. Combine that w/the assistance you can get here, that would be my choice I do believe.