Ray,
I have done a few briskets on offset smokers before I got married, and I remember that I ended up with a better finished product when running them 270-280 for the entire time. I know that is a tight window, but we had a great smoker that would hold the temp +/- 5 degrees. My buddy had it build for him from a gentleman here in the Rochester area and i must admit having access to it and trying to learn form him and others really has made it much easier. Now I must relearn on the MPS that I just picked up but I am going to be sure to at least start where I have had prior success. The 16 years between the time that I would be with buddies all day at a smoker, having adult beverages, and shooting the breeze and then having a wife and kids really seemed to put a dent in most of that knowledge that I had, plus not having a huge offset vs a vertical is a major difference too!
Dave