With general purpose, multi-band antennas such as yours, taking one band
with another, the higher the feedline impedance the less the loss in the
feedline.

This is because feedline attenuation in dB is directly proportional to R/Zo
where R is the resistance of the feedline conductors and Zo is the line
impedance. This simple relationship applies from 50-ohm coax (or lower) up
to 600-ohm (or more) wide-spaced open-wire line.

Ordinary 50-ohm coax is fine ONLY when the input impedance of the antenna is
itself approximately 50 ohms purely resistive and the line length is not
very long. But with multi-band antennas Zin is most unlikely to be anywhere
near 50-ohms on any band. It is more likely, taking one band with another,
to be several hundred ohms or even 1000 ohms with a high reactance
component.

Assuming the conductor resistance to be of the same order for both coax and
balanced-pair lines of the same length, line loss will be appreciably less
for the higher impedance lines. In fact, for the physical sizes usually
involved, spaced balanced wires have a lower conductor resistance than
ordinary coax and this swings the use of spaced lines further in their
favour.

Even a 300-ohm twin line with substantial conductors, not the flimsy old TV
downlead type, will effect an improvement over the usual sort of coax.
450-ohm ladder line is most popular because of cheapness and relative ease
of installation. But for perfectionists, on very long lines, a 5" or 6"
spaced 600-ohm work-of-art cannot be bettered.

With low-loss, high-Zo lines SWR on the line can usually be forgotten about.
But a high SWR can make severe demands on the tuner however.

Transmission line Zo, of course, is unrelated to antenna efficiency which
with a high antenna is nearly always good enough to be considered 100%.
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Reg, G4FGQ