Weight Loss and Heart rate

I wanted to ask this newsgroup a question about Weight Loss, and Heart Rate.

What is more beneficial, to ride long rides of say 50 to 80 kms, and keep
between my recommended training zone of 65% to 85% of my maximum heart rate,
or go faster and stay above 85% for a while, sometimes peaking to 95%.

Is this more beneficial if I work harder, or is it dangerous, what should I
do to acheive good weight loss ?
Thanks for any feedback.

Kazu