Hi Terry,
Any '.gz' suffix is not relevant when deciding how to output
and AFNI formatted dataset. Generally everything is ignored
from the final '+' and onward. For AFNI datasets, the
AFNI_COMPRESSOR and AFNI_AUTOGZIP variables are what control
the compression of the output, as you noted.
NIfTI is a special case in that regard when requesting output
of *.nii.gz; its rule does not apply to other formats.
- rick