IMHO
Effie is not really a natural nickname for
Stephanie.
Fannie is more natural than
Effie. It also seems artificial / affected to me, because it should be fairly obvious that
Effie was mostly considered a frumpy old-lady-name at the time you were born, but it is more fashionable seeming today. So, no, I wouldn't if I were you, unless it is purely for theatrical / pseudonymous purposes and people wouldn't call me
Effie to my face.
Personally I think
Stevie is cool, and
Stephanie itself is too, and
Stephanie does not really need to be shortened anyways.