Goliath predates bananas. They have no validity as a measurement in this circumstance.
Bananas were apparently first cultivated 7000 years ago, so Iβm afraid, based on Biblical chronology, that Goliath post-dates the banana (which predates the creation of the universe) and thus a banana for scale is a valid measurement for his height, as it is the standard reference for scale according to science I just made up.
TIL that both football and Oliver Smootβs fraternity pledge predate bananas.