RE: ARROW LENGTH
The 3/4" or 1" past the riser came from the days before shoot through risers. Now it's a matter of how comfortable you are with having a BH over your hand or trying to get proper spine. I use a 27" arrow out w/ a 30" DL to get a spine that is close with the GT XT Hunter 7595 w/ a 125 gr tip.
Accuracy is a matter of shooting form. With a lot of the very fast bows it's easy to make a small error in form and it affects the arrows a great deal.
Higher FOC arrows maintain momentum longer down range compared to a lower FOC arrow. This helps them psuh through wind better. However, that does not mean they are more accurate.
A higher FOC arrow will not go through branches better than a low FOC arrow. The blades hit the branch and either way it's getting deflected. That thought process goes with the old belief that a heavy bullet will bust thorugh brush better. However, a BH isn't round on the end nad has blades that catch on the branch.
Paul,
How short is your DL that you shot 21" arrows?
Number of pins is a preference that has nothing to do with how much practice you do or how fast your bow is. I used to shoot 1 pin on my old bow and now shoot 5 pins on a bow that is a lot faster. I practice about twice a week and shoot out to 60 yds some times. It was a personal preference.