This percentage will vary based on network conditions (active staking coins, masternode count, zPIV percentage), but usually rests between 8 and 10%.
In the past, staking rewards were 2 PIV per block, and masternodes would get 3 PIV per block. Now, with zPIV staking (private staking), masternodes can get either 2 or 3 PIV per block, depending on if it was PIV or zPIV that staked it. If a lot of zPIV are staking, masternode rewards drop down towards 2 PIV per block. According to the calculator linked by cryptno, masternodes average 2.8 PIV per block, which I imagine is pretty accurate, given that not too many people are staking zPIV at the moment.
On the staking side, I found their calculations to be accurate.
RE: Proof-of-What? Mining Incentives Matter, But So Does Fairness