Obryn
Hero
Erm... unless you only hit on a natural 20 or only miss on a natural 1, a +1 on a d20 is always a 5% change in probability. These are rare corner-cases in 4e, though.That +1 isn't 5% all of the time, though. It can be higher or lower depending upon the AC of your target.
Hawkeye
-O