I'm a lefty, I shoot mostly right wing feathers, but also have some arrows with LW. Most of my arrows are 4 fletch, but also have a lot with 3. I shoot em CF in, CF out. Doesnt matter in most cases, but some seem to shoot better CF in on certain bows. If I shoot one and it fly's a little wierd, I spin it around and shoot it CF in.
I do remember when I first started shooting, I tried CF in, and it did tighten my groups up considerably. More often than not when shooting a 3 fltch arrow, shoot CF in. I think bow tuning has a lot to do with it. If your bow and arrows are matched well, they shouls shoot good either way.