I did not find much info for the RetinaZ3, just a few hints from the
kernel-documentation.
You definetely have to use 
 video=retz3
for the rest, experiment a little...

5.1) video=
-----------

Syntax: video=<fbname>:<sub-options...>

The <fbname> parameter specifies the name of the frame buffer, valid
options are mifb', yber', 'virge', etz3' and lgen', provided
that the respective frame buffer devices have been compiled into the
kernel (or compiled as loadable modules). The behavior of the <fbname>
option was changed in 2.1.57 so it is now recommended to specify this
option.

The <sub-options> is a comma-separated list of the sub-options listed
below. This option is organized similar to the Atari version of the
"video"-option (4.1), but knows fewer sub-options.

5.1.2) depth
------------

Syntax: depth:<nr. of bit-planes>

Specify the number of bit-planes for the selected video-mode.

5.1.5) monitorcap:
-------------------

Syntax: monitorcap:<vmin>;<vmax>;<hmin>;<hmax>

This describes the capabilities of a multisync monitor. For now, only
the color frame buffer uses the settings of "monitorcap:".

  <vmin> and <vmax> are the minimum and maximum, resp., vertical frequencies
your monitor can work with, in Hz. <hmin> and <hmax> are the same for
the horizontal frequency, in kHz.

  The defaults are 50;90;15;38 (Generic Amiga multisync monitor).

