A 155 and a 163 feel noticeably different, regardless of lug length. The 163 will been easier to not wash out on sidehills, and gives you a little more time to pick a line. The 155 feels more playful with more front end lift.
From what I have seen, given equal rider weight, in the snow around here, a 155 3" (have ridden some 156 X3's) would not outgun a 163 2.4 in deep snow, and the 163" would be an "easier" sled to ride. It just doesn't have the footprint. We are not talking night and day tho, and it really depends who's riding it. I ride with my buddy's 163 X3 Turbo Pro without issue on a stock 163 - I just have a little more experience which makes up for my lack of equipment.
I understand this is in contrast to Scott's findings - so if nothing else, that would indicate they are very close. I weigh about 210 in gym clothes - always have thought, if I weighed 180, I would ride a 155 and probably be equal in performance.
