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).

