Some years ago I did some fairly extensive computer modeling and some controlled experiments on fletching effects. I found that the arrow stabilizing effect depends only on total feather area and degree of helical or offset -- feather shape and three or four fletch make no difference. Arrow drag also depends only on area and degree of helical -- there's no way to get one without the other.
Of course, there are other reasons to use or reject four fletch, like cost, ease of fletching, nocking, visibility, etc, but not stabilization.