Betterbottle makes 5 and 6 gal PET water bottles. I could only find a source for the 5 Gal, so that is what I tested.
Empty 674 gm
MR with water of 29 with peroxide 39!
Burst at 125 PSI.
Long period of plastic deformation at around 100 psi
It burst in the thin center with the ends remaining substantially thicker.
This means one could probably prevent the banana deformation and increase the pressure with a center overwrap.