You are correct on the points of impact, except for the 0 yardage�your arrow will impact 4" lower than where you aimed, or whatever measurement is between your sight and rest.

When thinking about arrows, it is important to consider what the application is�hunting or target. Honestly, I would stick around what you have now (400-450grains)....it is a good balance of speed, k/e and potential energy and by the way .8 change in k/e is nothing. The 525 grain arrow is heavy and will hit like an absolute hammer, but you will need to adjust your shot selction because of the drop and slower speeds. Even though the higher speed of the 307grain is attractive, mainly because the industry is soooooo caught up in selling speed, I wouldn't even consider it for hunting because of the loss of potential energy. Now for target, or 3D, I would use the lightest arrow I could shoot because a flatter shooting trajectory is alot more important than a lower amount of potential energy.

A comparision that may put it into perspective a little better is a ping-pong and golf ball test. Imagine you are standing 10ft in front of a person and they throw both balls at you...which will hurt the most upon impact and which do you think will travel the most distance? The reason why the golf ball carries more speed for a longer distance and hurts more, alot more, is potenial/stored energy due to the increase in weight it has over the lighter object.

As far as should you switch from the coated cable to an actual string and what would it do question, I would have to refer that question to a string maker. I personally have never switched them out, seen it done or heard of it being done(that is really old bow technology  ), but I don't see why it couldn't be done and I could only imagine that you would pick up a little speed from doing so due to it being lighter than the cable. Send Energywave an email and ask them about their thoughts on it. Fasteddie could answer it as well, but I don't know how often he gets on here.