I've done my fair share of penning and sorting. A reiner should have the basics for the fast turns, stop & go, and be light in the bridle. I've used reiners before but the one extra ingredient they need to have if you are doing it more then just to have some fun, is that they are cowy.
If your horse could care less about a cow then you will be having to direct him all the time which will slow you down considerably. Turn him loose with a small herd and watch him. He'll tell you if he is interested. I do that with each horse I will use for sorting. The other reason I do it is because some horses are afraid at first, especially when they are bumped by a cow or one runs at them. I would rather have them sort it out before I step in the saddle and a cow tries to run over him.