The only time I've used the HPGL2 Driver is for Illustrator line art projects, as I understand that it's a vector image driver rather than a raster image driver. Have you printed photographic images with it?
It came up in a thread on the Qimage list. For the past two years I have tested how the plain Z3100 with the PCL3 driver could print beyond the 109' limit. Someone else needed to print longer with the same equipment and raised the question on the Qimage list. I wrote that it wasn't possible. In the end he mentioned an advice from a HP serviceman to get the HPGL2 driver. He did and he could print longer from Qimage that way. As Qimage can't handle vector images and the question was about bitmap files it was clear to me that we were discussing pixels in this case. I didn't ask whether the driver used in the end was the HPGL2 driver or that installing the HPGL2 driver allowed the PCL3 driver to go beyond its normal limit. As far as I know HPGL2 can handle bitmaps etc in HP's PCL description.
Matt Nolan wrote this on that solution:
Success! Using the Z3100 HPGL2 driver I was able to print out a
3'x17' panorama using Qimage and it looks great. The driver offers a
maximum of 91 meters -- I didnt test it, but I suspect it may be
The next thing I want to test is Mike's suggestion of cutting up
gigapixel images in photoshop and then reassembling them in Qimage as
separate images printed on the same page. This is different than the
banner trick where Qimage cuts the image and tries to avoid the page
break (which doesnt work with the Z3100). So if this new technique
works, I dont see that there is anything standing in the way of
printing a 10,000 x 100,000 gigapixel image, or even larger, using
end of quote
There was someone who mentioned in a similar thread here that with the Z-PS models the HPGL2 driver is bundled and installed with the other software. Which may be the reason that the PS models do not have that length limitation with the PCL3 driver. At least my Z3200-PS can go beyond the 109' length limit. And possibly also allows the PS3 driver to go beyond the 129" limit while the driver menu says otherwise, the fact I expressed my surprise about in the message before this one.
One thing is sure, HP should have given a more transparent description on the length limitations in all the drivers it has for the Z models. By trial, error and accident the picture of what works and what not becomes clearer.