I bought the 4/3 AmpK for xmas (MedShort). I fall right in the middle of the weight size and it is just right, a little snug maybe. So if you are on the higher end, might want to consider going up, but each body type is different.
BTW, I've used it at Stinson and OB this winter, no problem at all for warmth, even tho it feels way thinner than my previous OLD O'Neill.



