I just swatched for the Favorite Cardigan in my sig.
I'm using Patons Classic Wool, rather than the ArtYarns Supermerino called for. The gauge is 18st and 26 rows = 4". I'm getting 20 st and 26 rows = 4 in. The Patons is a slightly lighter yarn - 223 yd/100g vs 208g/100g, so I'm not surprised, really. I'm hitting the gauge on the ball band exactly. I don't really want to go up a needle size because it is a lighter yarn, and this cardigan needs a firmer fabric to maintain its shape.
Right now, I'm washing the swatch to see what it will do. I'm thinking I'm going to go up a size knitting - the S is supposed to cast on at 24.4 in if it was stockinette, and with my gauge, the M casts on just a shade under 24 in. The swatch is very stretchy width-wise, which is good, because I want some serious negative ease.
I have enough yarn to do either size, so that's not a worry.
What to do, what to do....