You can mix the two together...the casein breaks down much slower so that will feed your muscles longer. Whey is quick and is perfect for post workout. But That is a lot of protein from shakes tho....~ 100 Grams? right? I try not to do more than 50 grams a day...with the rest of my 300 grams coming from real food. I would stick to a mix of the two after your workout. If you had to do a shake at night just do strait casein....but if I were you I would just eat some cottage cheese. I eat it every night right b4 bed. Just my 2 cents