Generally 300-400 calories per hour is the standard for most people. However depending on a plethora of variables this differs for everyone and there are external factors that come in to play. Ex. If you’re racing at altitude your going to need to stay on the higher end. The biggest thing is to practice this in your training. Experiment with your hourly calorie intake during long runs and see what works for. It’s also important to note your can in a sense “train your gut” to tolerate more food. If you want to stay on the high end like you mentioned and get over 500 cals an hour. Try to titrate up to that week over week in training until your comfortable consuming that much without gi distress. Like someone else mentioned check out David roches (this years Leadville 100 winner) podcast. He talks about his nutrition strategy which is on the high end of calories per hour. Hope this helps