"one pound on the foot is like 5 lbs in the pack"

As a bit of a skeptic I take a lot of those popular saying with a grain of salt.
Often enough they are a myth , for example the "sleeping naked is warmer..."
So a few years ago I looked that up and was able to find the original study by the US Army on that.
Can't find that PDF but from memory it was posted on an official US Army site.
Anyway the study came up with a number around that 5lbs mark.
A more recent study came to this conclusion :
"It was concluded that the mass of footwear resulted in an increase in the energy expenditure which was a factor 1.9–4.7 times greater than that of a kilogram of body mass, depending on sex and walking speed."
Note that it states "body mass" so a backpack (usually not having the center of gravity in the right spot) could be greater.
http://www.springerlink.com/content/u18032vm25770745/
Franco