My longest was 760+ miles in about 16 hrs. We were so hyped up to start our trip we could not stop. Started in Gueydan La. and spent night in Amarillo Tx. That included stopping to wait out rain in Dallas for more than a hour that did not stop. So we road through Dallas in the rain. We road a total of 4625mi in 10 days. We probably put around 400miles a day pretty easily. Mostly just enjoying the scenery and views. We would leave about 730am in morning and ride until about 500pm and stop and get a room and eat and rest or take in a little sights in the area. Went through 10 states all the way to 4 corners Ariz to Rocky mountain national park to Custer national park to Sturgis. It was an amazing ride. Hope to do another one one day soon.
Just do whats comfortable for you and dont worry about the miles you traveled per day. The main
thing is that you enjoy your self. But on Interstate you can knock down some miles if you need to be somewhere in a hurry. Back roads and 2 lanes 300 to 400 seems to be pretty easy.
PS I would suggest getting a good seat though!!!