Sounds about right. 75 is an average day for me. I've doubled that, but that was with favorable hills and wind.
Different people have different styles. Some people like to push themselves with a light load and/or long days. Some people prefer to stop early and spend more time off the bike. The longest I've heard of was one guy who sustained 120 miles/day and plenty of people do under 60.
Regardless, unless you're counting off the miles, you're likely to end up with something like a bell curve. Road conditions, places to get water, places to camp, stops, etc will all encourage shorter or longer days.