At competitions I like my briskets out of the cooker by 8am if possible. When I take them out I open the foil for 10-20 minutes to dump some heat and then they go into my Cambro until we are building our turn in box at 1:00pm. they are still way to hot to handle without gloves.
If you preheat the cooler with hot water, dump the water and dry the cooler, and then insulate the brisket with towels or clean newspaper it will be hot for several hours.
What time are you serving? At 275 you are looking at about 75 minutes per pound for the brisket. Just get up a little earlier and catch a nap while it's cooking
You can overlap the cook if that's more convenient. You may just have to add a little time to the ribs if you are opening the WSM a few times.