I have done a pattern comparison test with my 14" SBS (cylinder bore) vs a 26" with a modified choke.
I hate to break it to you but they shot very close to each other out to 30 yards. Federal was around 10"-12" Remington was an inch or two wider. With buffered 00 buckshot and 7 1/2 birdshot you would have had a hard time looking at the target and knowing which gun fired which load.
Unbuffered shot was a different story. That gave a very wide spread from the SBS. The 26" was a little tighter but not much.
I don't think it was the function of barrel length. It was the lack of a choke.
After my buddy finishes his midterms we might do another test with the full choke.