color gamut for your printer actually depends on a few things, type of ink being one of them.
Oranges, greys, and just about any "bright" color are the most affected. In all the years I ran a jv3, I never once ran an orange that I was pleased with ( Triangle inks, flexi 7.6)
Personally I would print color swatches in the range that I wanted, and go from there.
I did a TON of work for one of the racetracks, and gatorade was one of the sponsors, let me tell you what kind of nightmare that was...
It's all about knowing your printer and it's limitations, and then, not being afraid of just running mass swatches. Record those colors that you use alot and keep them handy so you don't need to go through it every time you get a difficult color.