I am told the G&G hop up unit itself is pretty decent. The issue with its hop up, like most, is that it uses a relatively stiff bucking and a standard nub. A softer bucking (45 degrees maybe a little more) and a H nub would potentially make the hop more consistent.
The barrel on the other hand is pretty standard affair in the G&G CM16, so a tighter precision barrel can certainly improve range at the cost of some accuracy. Its not entirely clear that either mod will necessarily improve anything, you may make things worse or gain no measurable performance at all.