RE: What is the lightest arrow on the market?
Adding weight to the back of your arrow (5" feather as opposed to 4") will reduce your FOC. Not that the difference in feather weight will mean too much difference.
Additionally with all of the weight you are shooting up front, I don't see any need for the extra length of the 5" feather. A 4" feather fletched with some offset will stabilize your arrows just fine.
As for the Gold Tip arrows, what gives you the impression that the tolerances are not held tightly? While I don't shoot the Expedition or XT shafts, the Pro shafts (gold band) have always proven to be extremely consistent in the several dozen that I have bought. Also if you look under the target shafts, you can get the Gold Tip Ultralight Pro 7595 shafts (8.5gpi).
Not this part is purely opinion....
While I sort of understand your desire for an all black shaft for the 3D course, especially if your buddies like to chase nocks, I can't see why you would want a completely black shaft for hunting. It would make finding the arrow, in the leaves and such after a pass thru nearly impossible. It will also make it significantly more difficult to determine the type of blood and thus the type of hit when you look at your shaft.