It's now scheduled for December 8.
I guess you can flash the complete XT905 firmware on the XT907. It did work for me and even the modem does work for GSM (no idea about LTE or CDMA though). It's just, that there is still no KitKat available, so a CM jbbl version would be needed.
Yes, basically RSD Lite only wipes the user data with this line in the XML:
If you have it in your file, just delete it and the user data in this partition should stay untouched. But you never know, so better have a backup anyway....
I thought logo.bin was locked along with boot & recovery?
Actually, the bootlogo is the only thing you can (cross-)flash with a locked bootloader. For example you could take the SoftBank logo out of a 201M *.xml.zip and flash it onto an XT907. It...
Android 4.1 has various security issues that won't be fixed anymore, so that's not really an option.
But I don't think there are big differences in battery life anyway (see this)....