competitors have different eyes, and as the national matches seem to be mostly under 18 or over 60 yrs old, there is a big selection in front sight posts that are CMP/HP legal that help people of different ages focus on the thing. size seems to make a big difference.
one of many examples of quality retailers:
http://www.whiteoakarmament.com/xcart/home.php?cat=287&sort=orderby&sort_direction=0&page=2
you can get a front sight post here that is .040 .045 .052 .062 .072 or standard width. they are $10. for that price, you might want to try a different one.
your choice of zero will depend entirely on what type of target you shoot. if you are shooting the standard national match bulls eyes, then you can do a center hold, 6 oclock hold, line of white, flat tire, reverse flat tire, etc. as far as distance, just about everyone uses a 100 yard zero.
if you're shooting some other type of target or a wide range of targets, e.g. plinking, then it gets a little more complicated. 6 oclock gives you the best view of the target, but isn't very precise since you have no idea how big your target will be. as far as distance, it is also more complicated, and you need to think about your offsets. i.e. if you're trying to hit the A zone on an IPSC head at 10 yards, you would normally hold the top of the head with a 50/200 yard zero, but how do you hold the top of the head with a 6 oclock sight picture? hmm.....