I have just opened my last bag of WGC. I would very much like to try the Picnic. Actually, since I know what you think of WG and recommend Picnic I just want a bunch of Picnic. I have to figure out getting it.
Yes, abandon any notion of a targeted finish temp. When the brisket hits the low 190s look at the clock. If it's been over 90 min since you foiled but not quite 2 hours you'll likely need more time, 30-45 min, but check the brisket. Don't move it--check it where it is. Keeping the crimp high, uncrimp carefully around the probe. Uncrimp enough so that you can probe in a few places to feel the meat. Check in the usual center area, not the tip nor the point. If there's some resistance, remove the probe, reseal and cook another 30 min or so and check again. There is more leeway, finish-wise, with briskets cooked this way--if you go 30 min but the brisket needed 15 no problem. I have been getting 12-pounders and the time in foil has been between a bit over 2 hours to 2:40.
Remember, too, that since you're cooking higher you'll get good residual cooking after pulling. Get a large cup measure ready and new foil. You will have scoped out the liquid quantity situation the first time you checked. If it seemed scant (not likely) have some chicken stock (or beef) ready. When the probe enters easily it's done, as you know. Carefully lift off the package and drain the juices into the measure (You could have as much as 3 c so be prepared. Wrap anew in doubled foil and stick a good 1.5 c back in there, unseparated. Separate and de-fat the remainder, if desired, for sauce (I separate the remainder and put some or all of the lean juices into the sauce or build a sauce from it directly, or both.)
Definitely let us know.
I have a 3.2-lb hunk of chuck in the cooker now. Cooking @ 310 at the moment. In the 170s I'll foil with onions, garlic and wine/balsamic/sherry reduction and a couple sprigs of thyme. Doing duck confit sous vide overnight tonight. I've been on a roll!