I was recently speaking with someone who told me that they preferred the sight radius on a 16" because the shorter sight radius was easier to see. For the past 3 years, I've used the ghost ring -same plane rear aperature sight on both 20" and 16". The XS Ghost Ring tactical sight(www.ashleyoutdoors.com) dramatically improves your sight picture and increase the speed of sight acquisition. For $30, I only changed out the rear and left the front post alone. It is truly an awesome modification to the standard sight and makes a tremendous difference when using iron sights.  Just wanted to share with those who are building, because it is the first modification I would make.  Just my .02

the XS Bog Dot sites are great looking for the AR's, but after looking at the XS web site, the AR front sites have to face towards the shooter to be effective, so any elevation adjustment must be done by completely rotating the front site post 360 degrees. This is opposed to the 90 degree quarter turns of the stock A2 front site post. This sound like the XS front site would be hard to zero with such a large movement up or down for each rotation in elevation. Am I just being over-analytical?

BWhalen, you're right about the front sight, which is why I only replace the rear with the ghost and leave the front alone. The ghost rear gives you a real quick pick up, is very easily seen when focusing on the front sight only.  It's easy on the eyes.