I am not sure why this in in this competetion forum, but if you want a serious answer, the 140 threshold is when the smoke ring stops forming. A brisket will take on smoke to a diminishing degree well beyond that point
If you want smack, my brisket can take on smoke longer than your brisket can.
Jim - Another transplanted Texan
Former KCBS CBJ
Large and Medium Big Green Eggs , Black 18.5" WSM, Blue Weber Performer - Stainless, Green Weber OTG Kettle , Brinkmann SnP Pro, and a Stainless UDS. One retired Portable Kitchen grill.
Red Thermapen, Maverick ET-732, EdgePro Apex Sharpener.
Avatar is the original 1951 Weber Kettle