When i got to 50 cp 0 i got two full set made in training gear. Since i did not want to bother people i kept this equipment till cp 160. By that time my weapon rune was doing only around 1000 dmg and when i changed it went over 2500. Of course my hp and magicka were down too.
So for my new sorcere i made gear at 18 and then at 30. at 28 she still had not real problem doing the group event in some public dungeons but it was time to change (again here run damage was down to around 1000).
So i m wondering what is the decay formula, now she is 37 and the level 30 gear still have rather decent stats. My guess is that it drops sharply when the level difference is 10 or more. Next for CP i don t know.