The stats you can get are somewhat dependant on level. The higher the level, the better the chance you have of getting stats in the upper range for that item. Someone else posted this in the old forum; Ariana confirmed it when trying for the lowest possible finish (in the wastelands at level 17).
If you are level 15 and wait til level 30, you will probably have an easier time getting good stats. If you waited til level 50, I doubt there would be much difference compared to level 30. I have not done any experimenting to test the actual values, or tried to see how many levels you would have to wait to make a significant difference.
Of course if you wait, you will need to make sure not to accidentally run your mouse over the armour case or hit the alt key. By the time you get to a higher level, you will probably have found (or had a monster drop) something just as good.
