The main difference is in the barrel. The 11-87 sporting models have pressure compensated barrels and the 1100's do not. However, the 11-87P barrel is designed to only fire heavy loads such as buck shot and slugs and have non pressure compensated barrels also but the gas orifice sizes are different then an 1100.
The gas orifices on these barrels are sized based on the length of the barrel and the intened load. I have little knowledge of the 1100 Tactical other then the fact that I understand the trend in sales to put the word Tactical on something to increase sales. Any model 1100 with the 18.5" or 22" 1100 "tactical" barrel becomes becomes an 1100 tactical as it performs exactly like the packaged weapon. Same thing goes for the 11-87. Once the 11-87P barrel is put on one it is a quazsi 11-87 P.
I would not trust either of the above guns to fight with. They must be fired from a solid shoulder to ensure they cycle. I can not trust them to cycle if I fire while moving to cover, over or around cover or I snap fire one and it is not from a solid shoulder.
However, there is hope. While at the factory in April I was able to test fire the Versa Max. I fired 25 rounds of target skeet loads. I fired all either one handed or from the hip, over my head, holding the gun with my arms fully extended out and I had 25 of 25 cycle perfectly. My arms were always loose so the weapon could recoil back. I am amazed that what I found out that day. No 1100 or 11-87 could have accomplished this.
Currently Remington Defense is offering the R12 for Military and Goverment sales only but I know for a fact that this weapon will be taking over for ineffective 11-87P in the very near future. It will not be long after that cilivian sales will follow. You can see it at www.remingtondefense.com
I am waiting so I hope the LE sales are soon.