Hi Lee
It was a while ago when I saw roo sinew, I beleive it was from the tail, it seemed very long which makes i a little easier to back a bow. I dont remember quite well, but like Erick said, no difference. I have used moose, elk, cow, antelope and deer and not a difference noticed either. now I use cow because its very accesible like you mentioned and I find it easier to process than most other sinews.