I'm 5'7", 150lbs athletic build. The size 38 fits me in a good tight "race fit". The 40 is a comfort fit, but I've got some extra material. I bought 1 size smaller than normal for this suit. I fit a size 40 for the Missile, GP Pro v1, and Spidi Warrior wind Pro. I definitely could not pull off a 38 in the Missile or GP Pro, so consider trying one size down.
For the v2: It is definitely made for the tucked race position. Brian's review is spot on. I have a little bit of butt sag, but everything fits in place well. The arms are slightly long (they come down to the wrist), and the calves are tight when first putting it on (I normally never have calf issues).
My only criticism is that the thigh/hip armor could be a little bigger.