Decoction mashing is great. Well, at least it's fun. I shall see whether it produces any special results.

My plan was to dough-in at 150, rest for 20 minutes, pull 6 quarts, raise that to 158 for ten and then to boil it for thirty.

That's basically what I did. There was some pertty significant temperature loss in the main mash, but I'm not terribly concerned. What I wanted was a long low temp mash for good attenuation; I got long and low temp. The decoction didn't even come close to a mash out temp--I hit only 158 when it was returned to the mash. But that's fine; if anything, given the cool mash, it's good because it rested at that temp about ten minutes before the sparge, which ensures that any unconverted starch from the cool mash was alpha-amylased out at 158.