I take you've found thumpertalk.com? Lot of discussion over tyre sizes. I have a feeling that 140 is recommended for s or E models, the SM model has a different swing arm and runs 150's although I can't see how this would allow a bigger tyre as the chain run will be the same?? Check the wheel offset and consider dishing the wheel over to the right (loosen LH spokes by 1 turn, tighten RH spokes by 1 turn.)
I currently run 13/44 which is just lower than the E's 14/47 My plan for gearing is to run a 15 on the front and have a 50 on the back on my trail wheels and a 38 on the road wheel. I think this will need two chains but at Gregs prices this is not a problem!