Well, the balance will definitely be changed. The 4 oz shaft will be more forward weighted obviously. Many people prefer the hit of a heavier shaft 4.0 - 4.3 ounces.
What you should focus on is what about the wood makes it more dense. The simplest thing to look at is the number of growth rings. It may be that the 4 oz shaft has more growth rings. See if the 4 oz shaft has a slightly darker color to it. It could be from deeper in a tree that was very large, underwent decades of compresssion, so is more dense even if the number of growth rings are the same.
What you should do is equip both with the same ferrule and tip and decide for yourself if they play differently and decide which one you prefer.
It definitely means something, and they definitely can play differently. But how different depends on a lot, and you will have to be the judge on if you can discern a difference to you. Two shafts from the same tree can have different properties and play differently because of what part of the tree it was made from.
My advice to you is use it as a learning experience, learn as much as you can about the properties of each shaft, and then you might realize you prefer one over the other because it suits your shooting style better or you like the feel better.
Kelly