Sticky

I don't think anyone would assume that bigger = more mass ot heavier.
I think people would assume that bigger means larger.

Bigger
http://dictionary.reference.com/browse/bigger
http://www.m-w.com/dictionary/bigger

Heavier
http://dictionary.reference.com/browse/heavier
http://www.m-w.com/dictionary/heavier

Mass
http://dictionary.reference.com/browse/mass
http://www.m-w.com/cgi-bin/dictionary
http://en.wikipedia.org/wiki/Mass


However, even if bigger meant more mass or heavier, the 767 is heavier than the 707.
Take a look at the theorists sites, here is an example
http://www.whatreallyhappened.com/boeing_707_767.html

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Sticky The Stickman