and were going to start a journey in Australia and finish in England, where would you go? Planning to do as much overland as is humanly possible, not too bothered about staying anywhere too long and on the whole would avoid major cities as they are boring...

I would work my way through Asia and possibly India - we spent 3 months in SE Asia, OZ and New Zealand and loved it

Blog link

http://lizandrichardsa.typepad.com/2007_adventures/

We did this in 1974 but took 3 months, thpough we were not seeing Australia or England.
Our Route was

Sydney - Bali
Bali one week
Bus through Indonesia to Jogjakarta & Jakarta
Jakarta - Singapore
Bus up the Malay peninsula to Penang (seeing the Brinchang Highlands)
Train up to Bangkok
Fly Bangkok to Nepal
Bus down to the Ganges Valley
Train along the Ganges Valley to Agra, Varanasi, & Delhi
Drive from Delhi through Pakistan, Afghanistan and Iran to Tehran
Bus from Tehran to Istanbul
Orient Express from Istanbul to London.

Of course, I would now avoid Afghanistan and Iran. I climbed around the Buddhas in Bamiyan that have now been talibanised. I would now spend time in Southern India. I would go more slowly through Turkey. I would visit the Eastern European countries that were part of the USSR when we passed through.
I would leave Australia from Darwin and go up there by train as much as possible.

John's trip sounds like a great "starter kit" for such an adventure: you can simply flesh out your version using his as a basis.

John, does the Orient Express layover in any places along the way or is it a straight shot?

Jeff,

This was 34 years ago. The Orient Express was just an ordinary train, not the romantic image the name conjures up. You could stop along the way if you wanted, but the soviet block countries wanted you to change a lot of money, and anyway, we were in a hurry at that stage. We did have a meal in the Turin station. It was a three day journey to London then.

I'm pretty certain that the current Orient Express has changed a lot from 1974.

There are several trains in different parts of the world that call themselves the Orient Express. Go figure.
John's itinerary is a very good "template".
I would however prioritize those destinations that have a foody culture. Cultures that attach an importance to food are always worthwhile. -- My prejudice.

I just had two months and spent it in Australia and NZ on 3 home exchanges. I couldn't imagine a 6 month trip moving around all the time as there would be so much stress.

That is, of course, just me. You do what you want. I had only 2 1/2 weeks in NZ and wish I had had more time there. I only did the North Island due to the location of the home exchange (NW of Auckland).