I've been running a 41 litre TT tank for quite a few years now. I find it perfect for travelling outback and anywhere else for that matter.
I usually end up with about 35 litres between stops but once last year I did 37.5 litres at which stage the fuel pump is just starting to hunt for fuel.
Generally speaking, you do notice the full tank, but one has to remember that it's after the bike has been running empty so you should feel the difference.
You have to rotate the fuel pump and also change a supplied metal wire, that holds the actual float.
I have seen and read about getting rid of the air reservoir at the top of the tank by drilling holes which allows one to hold 2 litres more fuel. Having seen what expanding fluid does to containers when it gets warm, I wouldn't suggest that it's a safe route.
Generally speaking I work to this standard, two up heavily loaded, sandy tracks 500 Klm's, normal tracks 600 Klm's, bitumen roads and hovering around 100 - 110 Km/h for touring, 650 Klm's. If I'm solo then add about 10% and if the bike is totally empty except for the rider add 15%.
I have actually done 770 Klm's on one tank. This was really an accident as the last town I was going to refuel at wasn't there, it was just an intersection of two roads, forcing me to travel sedately another 120 Klm's.
If you do fit it to an 1100 you will need to purchase early model 1100 tank rubbers. They are the rubbers between the tank and the fairing bits. My 1100 is a 98 model and I required the early rubbers. It doesn't fit exactly but good enough.
I would also strongly suggest if you haven't already done so, to fit the fuel lines with QD snap connectors. Things are a bit tight wiht the larger tank and reaching underneath to fit leaking lines isn't a really good idea.
If you fit the tank you will not regret it.
The Touratech tank bag also fits this tank perfectly