From your question, it sounds like you plan to foil for the rest only. If so, I would start probing for doneness when the thick end reaches around 190, but it may not be done 'til over 200. When it slides in like buttah, it's time to foil, wrap in a towel and rest in the cooler Make sure you're not probing in the fat line, I like to probe the thickest part of the flat.
If you do plan to foil for the last part of the cook, I would do it when the internal temperature reaches 165. Probe through the foil and remove to rest as per the instructions above.
In a good cooler, wrapped in a towel, the brisket can rest up to 4 or 5 hours and still be hot when you slice. Good luck!
Mister Bob, Pitmaster - Smokestack Lightning, Bad Ass Barbecue. KCBS CBJ #31759 - IMBAS Certified MOINK Baller