Both are super machines. We own a 900, and have put many hours in a 1100.
Don't think there is enough fuel comsuption difference to even throw the dice.
It is just what application you are using them for. In my case, the 900 fits the purpose. I'm in and out of the cab so much, the doors would be nothing but in my way.
Where I can see myself purchasing a 1100 if there were other things in my life going on other than the things I was doing. That cab air / heat would be a life saver for many..............