Just a quick update, it took nearly five hours to drop from 8% to a point where it decided to shutdown, so the battery calibration was definitely out.Battery life is definitely worse (<8h with minimal usage). Tried most recommended things (location rubbish off, Google Now disabled, powered down). Am now waiting for a full discharge. Not keen on the factory reset because of the bricking reports with earlier ROMs.
I then recharged overnight, and it's a whole lot better now. Still not as good as 4.0.4, but usable. I'll do another complete discharge and see if it improves further.
I really like the bar in the notification dropdown where all the major system settings can be accessed directly. My Nexus 7 doesn't have that, so I assume it's Samsung specific.