I normally listen to my music at fairly high levels on most phones. I have found that the Etymotics do allow me to listen at far lower volumes than any others though. I certainly wouldn't be too concerned about the levels that you listen at - I have the Panasonic 570 and regularly listen to the Ety's at levels far higher than yours.
I have found that with the Ety's you can start listening at low levels and then gently ramp the volume up until you find the right 'sound'. I would recommend that you don't particularly focus on what 'number' you are on - trust your ears!
It's fair to say that the Etymotics have the potential to save your ears from too much abuse of loud music - even headbangers like me can enjoy music at much lower volumes with them.
Perhaps they should be given out free by our National Health Service as preventative medicine.