Up first: an upgrade from Release Preview (build 8400) to RTM (build 9200) is not possible.
As so many people I installed the Developer Preview, the Consumer Preview, the Release Preview and the RTM. Every new version was a clean install from USB stick thanks to the USB/DVD downoad tool. Never had any problems with the previews, but the RTM showed “missing media driver”.
Turns out there is an old (2007) Windows XP post from Naxxfish giving me a workaround by adding the SATA driver to the USB stick. To extract the image I used 7-zip that supports the exe and the ima file. Running Windows 8 Build 9200 now.
I am still not getting the consumer preview on a USB. Will try the naxxfish workaround, thank you…