I wanted a setup similar to yours, I had a 3.5" niger, a 3" picasso, and a 3" White line trigger. At first the white line chased around the picasso, but after about 1.5 weeks the picasso fought back and REALLY REALLY beat up the white line. My tank was a 65 and it didn't have live rock, so I guess it was just dumb judgment on my part. The picasso and niger never fought at all though. Even after a year the two never bothered one another.
MakoFury