Today, a jogging partner suddenly said to me in the middle of a run, "You breathe in a 3-3 pattern eh?" He is an avid runner and a fast one too. He usually does a 2-2 pattern. That question prompted me to look into breathing patterns in running. A quick search turned up following references. They do not all agree with each other though.
So far, I do 3-3 in my warm ups and switch to 2-2 near the very end of a run. If I start doing 2-2 too early, it seems to strain my diaphragm too much with the frequent breathing. But I'll try to experiment a little bit in the future and see how different patterns work for me.