I have managed to downgrade but wasn't as straight forward as I'd have liked, first Flashtool had an error which I think was because I didn't have USB debugging on, I think with that on it installs an extra driver on the pc which then lets it install correctly...
Also after using PC Companion to back up my phone (and getting a 5.5gb file) when I then restored to my newly downgraded phone it only restored my pictures and videos, none of my apps or other data, it did say I had to manually install the apps again first for it to restore the data, and even when I did that it still didn't restore the data! lol
Not sure what the point of the phone back up is now
Also there are only a six themes to choose from, there were loads more on my original UK generic rom, the ones on this rom are pretty rubbish
But the good news is now my Star Wars Commander game is running smooth as silk again!