Preventing unwanted firmware update to REL11..help please

[morgoth123]

I picked up a Dutch SONY Google TV NSZ-GS7 device yesterday and would have liked to root it.
However I wanted to know my current firmware release and to know that the device has to be connected to the internet to be able to finish the initial setup and check the actual firmware version.
After checking my current firmware which was probably something like REL05_NSZGS7_EC2... (only REL05 i know for certain) the GS7 already downloaded and prepared the latest REL11_NSZGS7_EC2_2205_136227_20130807_URSC_S67254 to install without my knowledge and asked me to reboot. Obviously I do not want the update to REL11 to be installed since it will plug the security holes needed to root the device. I have a couple of questions.
1) I can get into recovery mode..will factory reset (formatting /data/chrome /data /cache ) make sure the downloaded update won't be installed anymore after reboot? Or has the update been downloaded elsewhere and will the firmware update still occur after reboot?
2) In case the factory reset won't help to prevent the update..will performing a software update from usb stick in the recovery menu do the trick? Obviously without rebooting first. Which means i need to rename a newer firmware than REL05 to update.zip .
3) Can anyone provide me a download of any release newer then REL05 but older then REL11? I think for example the file name for REL10 is REL10_NSZGS7_EC2_2203_133772_20130529_URSC_S67254 though I'm not 100% certain. In any case the firmware should be suitable for the Netherlands. Maybe someone can sniff the appropriate file at [Google Link] ... ony_beetle which seems to harbor all the firmware files.