Pack is basically the point at which the combination of the piston hole size/# and fluid viscosity no longer allows quick enough shock shaft movement to absorb whatever your hitting; in escence the shock is "locked up" over the smaller bumps and ruts and cannot travel far enough fast enough over larger stuff. On most tracks you want to be using at least 85-90 percent of your available travel to get around quickly.

On shocks, the further you stand em' up the less ressistence they have. The more you lay em' down, the better the car resists roll. The main thing to be weary of on the upper/lower mounting position is that you don't want the suspention to be hanging on the shocks. If you choose to use the upper holes, the droop will have to be raised and you will loose travel which is not horrible on a smooth/blue groove track that does'nt have any brutal obstacles but not wise on rough track with alot of divets, ruts and/or large jumps.