Hi, Tex
I own both, my 1100 is 20 + yrs old and runs like a champ, my 1187 is about 10 yrs old and the same. The main difference between the 2 is the 1187 has 4 gas ports and the 1100 has 2, also the 1187 has a stainless steel magazine tube which is part of the gas system. I have not seen the new 1100 apart, but suspect they have stainless steel magazines. The blue magazine tubes have a tendency to rust which makes it hard on the rubber seals and gas rings. If the gas ports are kept clean and the magazine tube kept clean and lubed, they are very reliable and softer shooting than a benelli. Also accessories are common between the two. Both have good triggers that can be improved easily. I set my 1100 up for 3 gun, and until I went to ghost ring sights was a winner. Once I went to ghost rings ( scattergun technologies and mmc) my times slowed quite a bit. I thought I needed more practice but it did'nt help much. I took my stock 1187, with trigger job, and speed feed and competed with it and my times went back down to what I normally expect. My normal accessories are, choate oversized cocking handle, vang oversized safety, choate magazine ( 10 round ) , speed feed loading gate, scattergun or wilson cartridge follower, trigger job ( 2 lbs), fiber optic front bead, good recoi pad, (sims laboratory is great), side saddle 6rd, for home use a surefire forend, and butt cuff shell holder. Sling optional.
I believe the 1187 4 port gas system was to allow use of low and high power cartridges without changing anything, I guess in the end it was not that much of an improvement.
NOTE: gas ports are the most common reason for failure to eject, and can lead to the extractor ripping part of the rim of the cartridge off. To clean properly, buy some pipe cleaners, available at tobacco shops or from brownells.com. soak in adequate solvent and really clean the ports after every 200 rounds. This also applies to the remington gas rifles.