I am waiting the P59 to be traded on CB, to be in convenient time of frequent rewards. Early investing is the most plummy.
From what I've observed in the reward table, profits will increase till 72000 block and then decrease. But you're right, early investing means investing when there are not many masternodes, so you get rewards more frequently. Risk is always here, but seems like being among 5-10 first MN pay offs really fast.