Yesterday i was downgrading from 6.35 to 6.31 on my psp 3000 09G whil i was downgrading the update stopped stopped at 80% and after a while it showed "update failed, contacct technical support" and then my PSP got bricked, which does prove that downgrading within a Psp's capabilities is also dangerous .
ProfanRVNV
EDIT:Got myself a new PSP