Having done it with cooking and camping gear as part of a cross-PA tour in basically 2.5 days, I wouldn't want to wed myself to 2 days or a 90 mile day. Day one was to Connellsville. Somewhere over 60 miles. Had a headwind the entire day, and it was warm and sticky. I felt like I had done a good amount of work for a rail-trail. Second day was to Rockwood. Also had a headwind. Day three I made it to Cumberland and continued on to Bedford, PA. Exertion and the potential for bad weather delaying you aside, it's nice to have some time to stop along the way and take in the sights. I spent a decent amount of time down by the river in Ohiopyle..

Ultimately, what is reasonable for you will depend entirely on you.