CPM is based on a number of factors, which usually include how long an ad plays, and the number of people who click on an ad. It's going to be different for different channels based on those things plus the category you're in and your demographics. To give you an example, we know someone with a 70/30 contract with fullscreen who is making roughly the same money after the 30% split that he was with adsense. On the flip side, if you are already getting a good rate with adsense, it may take a 90/10 split or better to equal what you're already getting with adsense. There's way too many variables to predict what you will get paid, so if you're worried, sign a short contract and leave if you don't like what they're paying out.