I've never had an aggressive sixline. And my new leopard is uber passive. I think, in general, wrasses are passive additions to community tanks, but as always, you sometimes get a weird one.
50/50 to me is too high. As someone who gets attached fast, I would find it very hard to bring it back to an LFS. I dunno if I would want that situation. There are other wrasses that are more docile right?