So wait.
Let me state what I think may be obvious to some, but not to me.
SadieKate...
the gist of what you are saying is:
ForeRunner: GPS elevation only. Much variation/error. Essentially worthless for elevation readings.
Edge: GPS and barometric elevation readings. Some variation/error. Generally more accurate than GPS alone. Not perfect, but okay for consumer grade.

(that is the general sense I've gotten from other folks over the year I've had my Edge, at any rate).