I agree with HighDesert to a point. Carbons do vary a lot more, but it depends on what quality of carbon you get. There are entry level adn up to and including excellent quality---priced accordingly I might add. You buy cheap ones that are straight within .006" and that means a total runout of .012". You get .003" (plenty good enough) and that's .006" runout. The biggest difference is that with carbon you don't need an arrow straightener---for obvious reasons. Yeh, aluminums are straighter to start with, but they don't stay that way.

Another matter is that if you have your arrows made or make them yourself all you need to do is cut 1 1/2" from the nock end, the rest from the point end and you end up with an arrow that is straighter, often making a .003" shaft nearly .001". And it'll stay that way unless you start banging on rocks and trees which will trash any arrow.

As for weight, I think 3 grains is really nitpicking. Have you ever weighed vanes? I've weighed some by certain manufacturers that varied as much as 4+ grains in a pack of 50 (4"). How many people really take the time or care to do this; yea, how many are even aware of it. Points can vary that much too. So in reality 3 grains between shafts ain't squat.