Instead of playing with the adaption threshold, you may try a lower  bucket size, higher shading rate and/or lower number of processes. The adaption threshold will just tell Poser when to switch to a lower bucket size, but Poser may ran out of memory  before that check kicks in.

For Poser 6 I switched the adaptive bucket size off completely as that would allow Poser to use more memory... Didn't try if Poser 7 has the same "problem", but you can try switching it off and see if it works, too.