I never cook brisket to a set temp. They just don't go that way. As you cook more of them, you'll find a better method. Sure you can use the temp as a target and it will serve you pretty well, but...
I call mine the stick method. Stick it with a temp probe and "feel" how tender it is. When you push it in, get a feel for it. As you slice it determine if that was tender enough. Do that through a few briskets, you'll know what your definition of tender is.