Here's my thoughts on barrel length.
If you are sticking a +5 or +6 Nordic tube on it why not go ahead and get the longer barrel? My +6 Nordic tube sticks out exactly 3/4" farther than my 26" barrel so you have to deal with the length anyway. So why not go ahead and fill that length with barrel? Like said you have to deal with it, so in the process get yourself a little more velocity and sight radius out of the deal. The velocity may be a moot point with 2 3/4" shells but if you stuff it with 3" or 3.5" turkey loads to blast a gobbler it might be a benefit. And the increased sight radius is dang sure helpful with slugs. I agree that 28" would be a bit much though.