questions about flashing a psp before tomorrow please

ive already hacked psps multiple times,but theres one thing im not sure of.
psp 1000-hackable.but what if its over the firmware 4.01?? does that make it brick if i try to flash the nand?? what if the 100 was higher than 4.01,lets say 5.5 or something.is there something inside the system updates that stops the psp 1000from being flashed??
i already know about the chicken thing or what ever for psp 300,but i dont wanna have to install it and keep doing it over everytime i tur the system on.
how can i tell wich psp 2000 is hackable??im buying it used( or 1000 if i cant find a 2000) from gamestop and i wanna know before i buy it.im guessing i just turn it on and if the 2000 model is 3.9 or lower it can be flashed right?? is there another method of knowing if its hackable??
thank..sorry for so many questions..better to be safe than sorry right..