The protein levels in soy milks versus regular milk are so close there will not be any advantage to the .5g extra in soy milk. What you want to be thinking about is that soy protein and whey protein effect the body differently. Traditionally, whey protein works exceptionally better for building lean muscle. There have been some studies that show that an excess of soy protein your diet will increase estrogen levels in your body, thus possibly minimizing fat loss and muscle gains.