I know you asked this question to WC'ers, but I'll chime in anyway. I don't think that's a bad cabin at all, given that you have a guarantee for a much better price! It's really not that far back, and the vibration police often talk about it being a problem only aft of the laundry rooms. I did just one leg in 2005, and was assigned, and paid for category E, as that was all that was available, in suite 900, ALL the way forward. When I got onboard, I asked if by chance there was something else lower and mid-ship available, and I got one on mid-ship on deck 6 or 7. I was so happy to get it that it never occurred to me to ask for a price adjustment! Given that we had the "storm of the century" in the Bass Straits on that cruise, I was more than happy to be mid-ship.