Is this your only car now? Or do you have something else to drive? There are guys out there doing pretty damn good paint work in their garages, if you are not in a hurry. I have the names of a couple of places, that do great work for reasonable money, let me do some checking and make sure the painters are still around. What it is matters so send me a note if you get a chance.
While I would advise strongly against Macco, it comes down to how long you will be keeping the car. Because of the poor way Macco preps the car before paint, their paint job will last about a year or maybe a little more, before it starts to fade, blister or just starts looking like crap. Now that depends on many factors, a simple color would last longer than a metallic.
I've seen a flat black hot rod that was done with a rattle can, looked pretty good because the prep was done properly. You know how long you keep your cars, if they tend to become totals in under 18 months, then Macco might not be the worst choice. If you keep them years or decades then listen to the other posters and go a little higher end.
The kind of car, German, Asian or Domestic is also important, sometimes they way it was painted wasn't really even paint in the classic sense. Some manufacturers use an electrostaticly charged power that is then baked into "paint".
Gunmetal gray is usually dark grey with a tint of blue, but did you mean more this
or this
If I remember correctly it was an OEM (original equipment manufacture) color for Honda, GM, BMW. I have a flat black obsession right now and really want to have my car "murdered out"
Car p0rn is almost as good as gun p0rn.