[quote name='thebrig' timestamp='1382624346' post='2254573']
... I am now suffering with incurable back problems, so I want to keep my new rig as light and as portable as possible ...
[/quote]
The MB500 is about the size and weight of a Jeffrey Archer paperback but much better value for money. Plus it will last a lot longer.
The Midget is the best & loudest cab, cubic inch for cubic inch, that I've ever heard, but I'm aware that this has become a very competitive part of the cab market. You may want to check out some of the others.
Incidentally, if weight is the sole issue you should know that the Midget weighs roughly the same as the Compact despite being roughly half the size. I used to play frequently with a Compact+Midget rig (you've played through it, remember?) and it always did my head in when carrying the two of them.