Tony,
What you heard about feeding a 'G5RV' more efficiently with
some type of 'ladder' line is correct. 'More efficient' is
relative though.
Just for 'grins', the 'ASL' height is sort of meaningless for
DX or local, makes little difference, in general. 'AGL' does
make a difference, since it is one of the factors which will
shape radiation pattern, impedance, etc. (If it's a choice
between a (+) ASL and a (-) ASL, I think I'd take the (+) one.)
'Doc