From a lot of experience...

From 1990 until 4 years ago I trained rigorously. Some years up to 4 hours per day. Your 'pace' time is excellent.

The greatest 'high' I can recall having in my life, physically, was when 'in shape' I'd have days in which I could run all day, and nearly did, several times. I'd be out on my 'normal' run... 5-6 miles, and get to the end and actually NOT want to quit.. and wouldn't. On those days I'd often run a full marathon distance and even further. Not for time... simply because it felt so great.

I used to describe those days like this: It was like being a passenger in a car. My body the car. I was simply along for the ride... enjoying the scenery as it passed by.