A further point about frame loop (magnetic) receiving performance is that
the near field is generally smaller than for a similar dimensioned (active)
(electric) vertical whip antenna. If neighbourhood QRM is a nuisance, then
a well-sited frame loop can generally outperform a well-sited active whip,
with the difference being the near field pattern. As others have commented,
the pre-amp noise figure is unlikely to show up as a limitation (relative to
QRN and QRM).
I have also found considerable mutual coupling between my top-loaded
vertical transmitting antenna (when tuned) and any LF receiving antenna I
have tried, anywhere within my suburban section. The near field of the
tuned transmitting antenna goes far beyond my own boundary! The practical
solution is to leave the vertical floating during LF receive.
73, Bob ZL2CA