You can check this out, Ive been collecting all the information I can http://narutoonline.wikia.com/wiki/Survival_Trial.

Personally, Ive just been doing Elite and stocking up my ultimate scroll due to my level being a bit low and there is a relationship between level and fragments you can get. But there is no harm in just doing Elite until there is more information out there and then possible using your stock piled ulitmate scrolls.

You are able to obtain Kage Treasure fragments from all Difficulties, including Normal.