You can get good loot with any ammount of EP, but if you have a higher ammount of EP then you have a higher potential of getting a good loot.
anything between 25% and 100% ep is all the same for me. just under 25% sucks. keep in mind that what you get from drops also depends alot on what you've lost on previous deaths.
Depends on your combat level as well. From my experience, the higher the combat level the better drops, without needing 25% ep+