I wanted to seed some endophyte free fescue into existing K 31 pastures this fall, but was told by the seed supplier that it wouldn't be able to compete with the K 31. That it would just get shouldered aside by the more robust K 31 plants. Also that it was expensive and that my money would be better spent on establishing more clover instead. Everybody tells me, if there is K 31 on the other side of the fence, or if you feed K 31 hay in a pasture, that is what you are going to wind up with. Even your mower, baler or bush hog can bring in the seeds and ruin your stand.
I'm going with red clover.