Let's assume you have 100 users who're returning back to your faucet constantly.
Now, let's assume everyone will come back 10 times, so you can form your CPM.
If you reward 100 users x 10 times x 99 satoshi, you'll be looking at a CPM of 99000 satoshi.
0.00099000 Bitcoin equals
0.76 US Dollar
You need to make sure you understand what you really want.
You need to give rewards based on your income. First start with low payouts, then see if you can afford to increase payouts, as your traffic increases.
No one can know your CPM, since no one can know the traffic you'll be having on the site.
It all depends on country TIERs.
Don't expect users from USA claiming 99 satoshi per hour ;p