I just hand tested the two 1.4x extenders on a 70-200mm f/2.8 IS II. I'll note that the 1.4x Mark II to Mark III performance is on par with or slightly better. I noticed a slight improvement outdoors with the III over the II, but nothing noticeable indoors/dim lighting. The store owner said that she felt there wasn't a significant difference between the two for the 1.4x, but in the 2x range, the III was the only way to go - 20-25% improvement on sharpness and photo quality. She did mention something I didn't look at - there are 4 screws securing the 1.4x II, and 7 on the III, and said she had less returns on the III (1) for mechanical/bad quality faults in the same time period (one year of release) and the II (4). Take that for what you will.
I live in Australia and I actually purchase my equipment from B&H USA. They were my dealer in the States, and they still remain my dealer here in Australia. I just ordered $184 dollars worth (converted and including shipping) of two Canon lens hoods, a Hoya 77mm ND filter kit and an additional UV filter. I priced them here locally for $430.
You can guarantee that the equipment you are purchasing isn't from Hong Kong, grey market or otherwise, and Canon warranties their lenses purchased from the US in Australia and worldwide. Be careful about ordering camera bodies from the States though, they need to be sent back to the US for repair work.
Australian customs limits your purchases by imposing Customs duty on a package worth over $1000. If your items are less than $1000 - converted, no duty and no fees. Anything over (like my 70-200mm f/2.8 II IS did at $2700 inclusive of duties) will incur fees. Even still, it was $500 cheaper than the quote from the local dealer.