I just saw this calculator on another blog (sorry, I've lost track of where!// Update! Neoprene Wedgie is my source! Thanks for the link!) and I thought it was interesting to play with:
Predicted effect of weight change on running speed
It seems to use a factor of 3 seconds per pound of body weight per mile; whereas I've always heard that the difference is 2 seconds per pound of body weight per mile. And it only gives you information for plus or minus 4 pounds. But interesting, nevertheless!!!
Free speed with weight loss. Simple physics.
Let that be an incentive to me as I work off another ten big ones before Ironman Florida!