in this specific case, it would be redundant with a 720 in the mix. An additional plus is the Genesis upgrade which is compatible with both of the units you are looking at but at this moment, more expoitable on the 720 platform. ARC is good already but Genesis seems to have lots of tunability, flexibility (Apple compatible!) that previous ARC didn't. Great news is Genesis is compatible with all of our goods including BF, Dynamo 1500, etc.
For you, the question is what else does the 800/1100 offer. The phone app is what I touch almost daily as recording levels between channels, recordings means making quick changes very easy. They are also pretty dramatic improvements over the older Dynamo subs so you are getting a better sub regardless of features on board.