I'd say closer to 8-10 hours at 275 and 6-7 hours at 300. These are all arbitrary numbers though as it will be done when it's done.
Just to add, when cooking a brisket at these temps you have to be more on-the-ball when checking for tenderness, so I would start checking at 190 IT and every couple degrees until tender.
I don't think you can peg a time on this method with any semblance of conviction. It's going to be done when it wants to be done. Half-hour a pound at 275? I seriously doubt it: unlikely could get to temp, but even if it does, the collagen hasn't had a chance to fully break down, and it's probably going to be like chewing on rubber bands. 275 is more closely aligned with 2 to 3 fold the time you laid out in your question. Stalls are individualized: some do, some don't. If you don't want good bark, wrap. If you do want good bark, don't wrap.
I don't disagree with your point, Duke: I do disagree that bigsmoke can get a 12 lb packer to fruition in a 6 hour timeline at 275-300. Not going to happen--that slab of beef will be inedible within that temp range. I completely concur with what you and I both said earlier: it's done when it's done.
bigsmoke: I did some digging around and found a post on a brisket I smoked at 275 last summer. A 13lb packer took me 12 hours + rest at that temp. gr0uch0 is about bang on.
http://www.smokingmeatforums.com/t/250209/birthday-brisket
My pleasure, bigsmoke. Don't rush perfection: I get as antsy as the next guy and want to sink my teeth into it asap, but there's reasons this crappy cut of beef is done at a snail's pace. Trust the process. Where you at in TX?
