I had a look at the iPad Mini on the weekend, and given the Mini appears to be recommended by the Ozrunways people and acceptable to CASA, it seems the best option.
The screen appears large enough to be useful and the nominal 10 hour battery life is good. The Mini also appears to be a good size to fit in a knee-board.
A quick check shows that the iPad Mini is being released in a "couple" of months, so I might wait a while longer for that.