Unless it is the extreme ends of the grading scale like Almost Prime and Barely Select there aint enough difference to warrant the expense. Beef is graded higher up and farther back than the brisket ( IRC between the 4-5 rib) it is fine for the higher cuts where the marbling is more pronounced. On a Brisket not so much because it is exercised more and essential to the movement of the animal so the marbling is very close between the grades. I have cooked Select & Choice side by side on more than on occasion and gotten a better product from the Select about 50 % of the time.
I'm a Proxy Vegetarian> Cows eat grass & I eat cows.