I have always run every sled of mine in the narrowest position, us 155 pounders need all the help we can get.
The story changed last spring however... I kept noticing these pros really need to be tipped over far to surf turn in the slush, and i kept burying spindles, and having the sled pivot (whip) around on me. I switched to the wide setting on 1 pro, and left the other narrow. World of difference! there was better ski response, and better angle to keep the spindle out of the slush in the wider setting.
I have been on 5 rides this year, and just now realized all 3 of my pros have the skis in the wide stance.
Maybe it doesn't matter in the powder as much, as my 100 pound girlfriend was throwing them around no problem (insert proddy stick figure here).
I will put one back to narrow, and see how noticeable it is in the powder.
I also pull my swaybars, but rode a friends with his on last Sunday. With a swaybar it takes a little less ski and rider input to finish a turn, but is less forgiving sidehilling.
Maybe remember the wide ski trick for the spring!