Not too sure what is the difference between the IQ5000 Trizone (http://www.myer.com.au/shop/mystore/beauty/womens-grooming/o…) and the normal IQ5000 (http://www.myer.com.au/shop/mystore/au-oralb-triumph-5000-sm…) as they originally have the same price of $239 on Myers website.
Shavershop have the IQ5000DH (Dual handle) for $189 which is better value I believe:
http://www.shavershop.com.au/online-store/oral-care/electric…
IQ7000 for $179:
http://www.shavershop.com.au/online-store/oral-care/electric…
The difference between the Trizone 5000 and the IQ5000 is what toothbrush tips come with the unit.
The Trizone 5000 comes with the Trizone tips which move side to side which means you need to manually "move" the handle as if you were brushing using a manual toothbrush.
The IQ5000 comes with tips that oscillate (round and round) which means the handle does the work for you. Aka. you don't "move" the handle. You just position the handle and let it do the clean and move it to the next spot.
Internally all models you listed are the same. Battery, speed, movement and cleaning modes. (40,000 Oscillation "round and round", 8,800 Pulsation "in and out"). Apart from the IQ7000 which has 1 extra cleaning mode.
You can interchange tips with any/all Oral B models. Trizone on IQ and vice versa.
Best value would be the dual handle pack from shavershop. Even if you are buying for a single person, as the lifespan of Oral-B handles are approx 3-4 years as they have NI-MH batteries and they will "die" sooner rather than later. Works out to be approx $90 a handle.
Hope that helps.