Not sure about Oreo dunking but I do know about graham cracker dunking. I dunk my graham crackers in fat free milk as the absorption rate is faster than with 2%. This allows me to avoid the situation where the graham cracker falls into the milk before it makes it into my mouth (perhaps I have learned the amount of time the absorption takes place with my fat free milk
). Additionally the reason for my graham cracker consumption is that when I wake up at 2 AM, after eating 2 to 3 half grahams with my fat free milk I can go right back to sleep.