A number of people have posted that the WM 'calories burned' numbers are significantly higher than what their HRMs show. I think the consensus was the WM numbers are inaccurate. I'd go w/ your HRM numbers. HTH!
I always find that for cardio the WM underestimates and that for weight lifting it is either right on or a little bit low. I question the numbers on my heart rate monitor too but they seem more accurate than anything else.