Thanks - you have all given me different things to think about.
Gut goes strongly with the 24-70 after seeing some shots from it on the K-1, as it does go wider than I currently have and covers all of my most liked range, but it IS expensive.
I'll have to do some research on the 28-105, but I didn't enjoy the 18-135 on APSC and so am a bit hesitant to go for a similar range on FF.
The Australian launch is next week and they'll have the lenses there to handle and try on the K-1, so it might be worth the trip to Sydney to help decide.