Ok, I've googled BMI and found the CDC website http://www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi.htm
that, at 6'8'' and 170lbs, told me my BMI is 18.7, borderline underweighted !
Granted, I'm really thin ! But I seriously don't think more sheer strenght would help my skiing. I'm certainly not an expert, but a competent recreational skier since my pre-teens years (I'm now 39). I can drive a high end ski and enjoy it, though not up to its full potential because of my technical limitations. I usualy run out of breath before I run out of legs actualy. Being a smoker may explain it...
I'm really skeptical of this BMI stuff, as it doesn't take into account the fat/muscle ratio. I'm all flesh and bones, I don't get fat, never. (Call me lucky, I can just eat all I want and burn it naturally !
: ). So those 170lbs are 170lbs of muscles on a tall skeleton... It may looks underweighted, but I wouldn't be a better skier with 60lbs of fat around my belly, maybe faster on a straight line, that's all.