I think in part the brisket takes so long because of the intense thermal mass and t-delta times. If I were to shave a brisket down into a slab that was 2 inches, by 5 inches, by 1 inch, it wouldn't take 36 hours to go grey inside.

https://www.seriouseats.com/sous-vide-barbecue-smoked-bbq-brisket-texas-recipe

With the heat so low as 135f, it was possible to still get a grey result. So what I'm thinking is find something between 135f-150f and 4-12 hours that gets the grey result with the lowest possible temperature.

I'm starting to think I'm going to have to go find a cheap cut of steak to buy and run an experiment. Figure out myself and share back results on "Stealth medium-well" steaks.