You got an exellent answer from Mark Manley so actually there is not much to add. Just beware that both for Myanmar and Thailand guides and permits are mandatory and its needed to be arranged in advance. And its rather expensive too. Especially if you plan to spend some time in the country.

Although the enforcing of these laws at the bordercrossings into Thailand have been rather incomplete, the one and only bordercrossing between Myanmar and Thailand at Myawaddy/Mae Sot allowed for overlanders do definetively enforce these new laws. So for the moment it doesnt look bright if thinking about doing this without guide/permits. An option is to aim for a short crossing into Laos or Cambodia and then re-enter Thailand without guide and permit, something that looks possible for the moment. That will allow you at least 30 days in the country freely roaming around.

Its also a question what you plan to do after Thailand? Shipping the bikes back? Continue to Australia? Ride the bikes back?

I also like the Honda CB500X. Great and reliable allround bike with fantastic fuel milage. It is a bit heavy for what it is though and if I were you I would fit some 80/20 or 70/30 tires on it to be more comfy hitting rough roads.

I would echo some of what mollydog pointed out. Set up the bike the way you think you'd want it and then take a small trip on it and see if your bum hurts, the windshield is doing its thing right, your legs are comfortable, etc. The bike will be a great tourer for you if you set up the ergonomics right on it. An aftermarket seat, lowering pegs and bar risers could be the small changes you'd need (or not) besides the right set of tires for your destination. The CB500X is a very capable machine.

Thanks very much everyone for your responses. I am disappointed to hear about Myanmar and Thailand requiring guides. We would have liked to stay for a week or so with our friend in Northern Thailand, this would be out of the question. I had already read that Iran requires a uk passport holder to have a guide. What a pain. I will have to do more research on our route. Does anyone know of companies who run tours of groups of motorcyclists through Myanmar?

There should be information about companies that provide guides and permits for Myanmar in this Facebook-group:

https://m.facebook.com/groups/152596798515738

Note that a week or two ago the bordercrossings between India and Myanmar «opend up» in that sense that overland travelling with a backpack etc without permit was allowed. With a foreign vehicle you still need permit and guides.

For Thailand there is also a Facebook-group about the new situation since 2016:

https://m.facebook.com/groups/1024579897597702