I only cased the bike once that I am sure of. That was sort of an extreme circumstance, and one wouldnt bottom or case as long as the suspension is right. Rooney's front and rear wheels both had 300mm of travel.
The slightly added weight of a late model rear end could be mitigated by the fact you dont have to extend both a swingarm and a driveshaft. Thats nice, all that work is done at least.
One would want to lace an 18" rear on the rear anyway, so you'd probably put a lighter rim on anyway.
Why do we think we are limited to 245 rear travel with the 1100? Is that the angle limit of the shaft? I seem to think it will do more than that if you hang the right shock on it. It will just a be a custom one, but then, you'd be making your own top mount anyway, so you will be anyway, right? Unless you just try and use the 1100 shock as well with a differnet spring, but then how you mount the shock might give you some different room, too... it really gets kinda mind blowing, quickly.