Not sure about the actual percentages, but since we had the twins my wife and I have been keeping the house warmer at night and I just had to go get a few humidifiers for the nursery and my master bedroom. I was waking up very, very dry and my wife said my snoring was off the chart. Since putting the humidifier in my bedroom the snoring has stopped.
I think you can just go by whatever feels comfortable to you and if you start to wake up feeling really dry or get a nosebleed you need to raise the humidity a little.