@okkipp I just made my first batch of summer sausage over New Years. I used the 2.4" fib casings. Doing the same 125/140/155/170 schedule using my Dad’s 30" Masterbuilt, it took almost 10 hours to get to 160 internal temp. But I think I may have had a little too much water in the mix, which meant longer time time evaporate it out of the summer sausage and allow the meat to get to temp. But, just like smoking any meat — It’s Done When It’s Done. You want to go by internal temp of the meat, not the time.
Another thing that may have lead to such a long time to get to temp, I had 21 summer sausages hanging in that 30" smoker. So there wasn’t a lot of empty space. I have the 40" Masterbuilt and I think with the extra room, I would have had a little more space between sausages, which might have helped with getting them to temp quicker.