I do have an answer for you and it's straight from the horses mouth...
What is the difference between the Model 1100 and Model 1187?
In 1987, the new gas compensated 1187 was introduced. The 1100 and the 1187 are similar in design. The only difference is the 1100 can shoot only 2 3/4" or 3" shells depending on the model, and the 1187 Premier you can shoot both 2 3/4 and 3" shells. Barrels are not interchangeable between these models. "
Doesn't seem to be much of any difference except for the above. I even reviewed the parts diagram for both models. The 1100(93 parts) has four more parts than the 11-87(89 parts). Still, the fact that you can shoot both types of shells in the 11-87 seems like a big advantage to me. I think that the 1100 only has one gas porting hole and the 11-87 has two.
Exploded parts list is in back of the manual at www.remington.com/pdfs/om...001187.pdf
Hope it helps.