80-100 is just fine with four bags, good roads, no head wind, in shape and not too interested in seeing sights.
Toss in some head winds or junky road surfaces and you will have to balance it with less weight or greater fitness.
As for rest days I start all my > then three week trips the same.
Three big or four medium days -> rest. Take another rest day 5-7 days after the first. Then as needed. I try and pre schedule a long period off every 5-6 weeks. (aka mooch a bed from a FAOF)