Grows faster (on paper, mine does not) height uniformity is compromised.

 

What about a Rye that would die off in the winter?

 

I haven't found that a cover crop is necessary. If you do everything right with your reno the kbg will come in nicely on its own. Also, can you get annual rye grass that is weed free? Seems like there would not be a very big market for that.

 

Prg survives my winter just fine. I don't want it in my yard, so I won't seed it with kbg.

 

Rye wont die in many places, even those that get smothered in snow all winter like @wardconnor when he was growing rye . I wouldnt bet on it dying where you live if you want pure KBG plant pure KBG. If it doesnt work out you can always add Rye into the mix with an overseed, you cant selectively remove it once its there.