I've tried looking and researching in vain for all answers for Skim Milk.
Anyone is welcome to correct me, but from what I gather lactose is a low GI carb. Milk has a high(or higher than it appears it should) insulin response due to its protein, specifically Leucine, the other two BCAA's and Lysine.
As far as lactose, technically any carb is sugar (right? the family of C-H-O's...they are all variations of the same chain?) and the "ose" ending should't always be a "trouble sign". Even a fiber like "cellulose", well, ends in "ose". Also not all of lactose is broken down into glucose as some is broken down to galactose (sp?) which doesn't stimulate an insulin response.
Anyway, I have no idea how all that plays out in your body and I have no idea if I helped or confused you. But from everything I've been able to piece to together the lactose isn't a problem. I would assume 50g of carbs you are getting wouldn't be a problem since you are getting other health benifits like protein from the milk. It might be wiser to have 4 8oz servings than 2 16oz ones.