I dont know what other people expectations are for next year, but something around Columbus and New Jersey is what I expect.
Around a .500 team. Perhaps lots of OT/SO games. A big improvement points wise in the standings. A 30-40 goal improvement on offense. 50-60 less goals improvement on defense. Still finishing 5-7 overall with a chance at the top 3. In fact, Im expecting the hockey gods to reward us with a lottery position win as a big middle finger to the league.
Given the changes in goal differential you cite above, I agree BUF would slot in around the current Carolina / New Jersey / Columbus range of finish. However, not knowing your fullset of assumptions, I think that is too optimistic for BUF to achieve next season. I don't believe there will be enough improvement in possession to improve a whole goal-per-game in goal differential in 1 year.
Even with substantial improvement, I think this is a bottom 5 team next season.
Adds: Kane, Reinhart, McEichel, probably Larsson.
Plus growth and better role / assignments / linemates for most of the forwards who remain.
Now, if Sekera/similar and O'Reilly/similar are added, pushing McCabe / Zadarov to bottom pair, and enabling McEichel (or Reinhart) to start season on the wing, then maybe your view is possible.
Your view is a lot more feasible if BUF lands a Cam Talbot / Ben Bishop vs. a Niemi / Neuvirth / Enroth / Lindback, etc.
A 0.01 higher save % from Talbot or Bishop on a full season's worth of shots would be enough to help the goal differential another 25 goals or so.
We'll see. Bottom line is, the objective shifts this offseason. We are building as fast as possible now.