The six-line's been in the tank for ... about three months now; he was added early on, shortly after the clownfish. The most that this particular six-line has done is harass my cleaner shrimp when they were smaller. (It's ignored my sexy shrimp, but, then, they usually hide in a hammer coral during the day.) In any case, I'd rather have the six-line; he's an aceol flatworm vacuum, to the point where I just don't have to worry about them, and that kinda service is invaluable.
And, yeah, I was thinking a M/F pair of McCoskers, after looking around.
Hrm. The six-line hasn't displayed any aggression to other fish in the past, but, then, I also haven't had any other wrasses in the tank. Hrmph. Do you think it's worth taking a chance while keeping an eye on them -- I take it that this tends to be more of a harass-and-pick campaign than all out fights-to-the-death -- or is it just a Bad Idea, not worth risking?