Thank you for writing back. The temperature difference between the supply water and the water in the pool might only be 1 to 3 degrees. It depends on how fast the water in moving through the pipes. 1.5 HP pumps will move the water pretty fast if there are not many restrictions. you performance look right for this time of the year. you are also correct that you will need a blanket on the pool in September as without it you will lose too much heat at night and then the heater will run all day to make up what was lost over night. If you have a cold clear fall night in NJ you can lose 10 degrees in the water and that is just a waste of money. My test pool in Washington right now has the 105 on it and it has about a 1 + degree per hour rise. I have about 1/3 the water that you do so the performance is the same.
Please let me know if you have anymore questions I can help you with.