Some reading on performace and calories...

A simple calculator (for which I am doubtful):

http://www.triathlontrainingblog.com/?page_id=483

Has some formulas that I will have to check more closely in other places.

Seems like VO2max is an important parameter in how one burns calories...

http://www.brianmac.co.uk/vo2max.htm#vo2 seems like a nice in-depth discussion.