Baylian,
Here's some nice web based ballistic apps to help you out,
JBM Ballistics.
For me, it depends on the actual caliber. For a flat shooting magnum, I like a 250 yard zero. For a standard caliber, I like a 200 yard zero. That usually means a standard caliber is about 2 1/4" high at 100 yards and a mag is 2 1/2" high at 100. I also don't like bullet to go much more than 2.5" above the line of sight.