I weigh 145. 700 kcals is about "tempo" effort: hard, but still fun-hard. All out, in the best shape of my life for one hour is around 900 kcals. I'm in good, but not phenomenal shape; my brief flirtations with road racing ended in utter humiliation.

I know this because of my on-bike power meter, which measures mechanical work in kJ. That "perfect hour" was around 280 W, and I've done it twice. (Cyclists have a very narrow range of biological efficiencies, so you can just multiply mechanical by a constant to reckon metabolic work.)