Well, at the risk of starting a brisket war, you should get the brisket up to at least 205 degrees to be ready. For steak, 145 is good. Not so much for BBQ brisket.
Now, the fact is, brisket is ready when it's ready. However, when I cook it, it's ready to rest in foil for 2 hours once it reaches 205 degrees in the thickest section.
I am a proud brisket temperature taker. It works well for me.
Operation BBQ Relief Founding Member - I am Obsessive Compulsive about BBQ. Google it.