That is incredibly good. Only you know if it's better than the Mining Game as you know how much it costed you to get those refs xD. Assuming 3k coins per hour as you said, if it costed you less than 5.1m coins ($510), then it's better, if it costed more, then it's worse.
Then again I don't know how accurate and how consistent is that 3k CpH you claim and keep in mind Mining Game earnings are objectively consistent (If you have 102k MP you will ALWAYS make 3k coins every hour, doesn't vary and doesn't depend on anything).

Oh, also I forgot to add Pool Shares to my calculations, which is very important. So yeah, Mining Game is a very good investment, maybe even too good to be true xD I hope nothing bad happens.