I flew in row 16 on a 321 CPH-ARN a couple of days ago and it was tight but no worse than a MD.
Recently I was in C to LHR on a 321 and got the bulkhead on the left. Here the bonus is in the wider seats. However, I moved back a row because it was empty but was not too impressed by the pitch. Surprised if it really is 3" better than economy.
If you are flying in C then definitely go for the 321 over a MD. Laptop power is nice as well. I was in row 2 on a MD-90 recently and it was quite uncomfortable.
Are the 321s that fly intra-Scandinavia different from those that fly elsewhere with C class? You can redo the seat width but probably not the pitch. SK only has 5 or 6 of these planes.