I agree with GLH and coffeebluff - Go as low and slow as you possibly can. Let that fat render out and through the meat, don't rush it if you don't have to.
In my opinion, beef takes and holds smoke better than pork. I've never over-smoked a butt but have a brisket. Eight oz of Mesquite sounds like over-kill. Like coffeebluff said, cut Mesquite in half (at least) and combine with a milder wood like pecan or oak.
Brisket should stay nice and warm in a cooler for four hours.
Let us know how it works out.
Good luck!