I followed this thread. My point in posting my experience was that *IT APPEARS* I didn't need to flash the ROM... I just used command "fastboot boot boot.img" and it did its thing. Idk what happened to make that happen but how I read the OP guide it doesn't seem it means to work like that.
So what I did. I have ADB/Fastboot setup in a folder on my C: drive. I put the extracted boot.img from the ROM of my choice into that folder and hooked up my phone to my laptop.
I then booted into Fastboot mode and used the Fastboot command as described in OP. After that my phone went into "Know-it-all" mode and just booted up the ROM.
If I need to clarify I can as I wrote this from memory.
Just my spare change.