Hi David,
Bertrand is spot on about getting the same bike.
My husband is 6'2'' while I am a midget 5'4'' (on a good day). Choosing travel bikes has always been about compromise.
For south America we had two BMW GS 650. Fine for Alistair but way too heavy for me.
In Vietnam we rented 2 YBR 125 and I discovered how fun off-road could be.
For Mongolia I wanted a more enduro type bike. We took 2 Honda XR125. Perfect off road but too slow on normal roads, crossing Europe or Russia.
For our next trip (Russia next year) we decided that 250cc would be the ultimate size for a travel bike, fast enough on tarmac and light enough off road.
I bought a TTR 250 last summer, but I failed to lower it enough for me, the shock is simply not sagging even after adjusting it to lowest preload setting. And I am not buying a new shock!
So we are going to break our golden rule; i.e. travel with the same bikes!
I bought an XT250 (grey import from Japan – 2009 model with Fuel injection).
Ideally having the same bike has always been very useful to us as when one breaks down, and it will happen, we can use the other as template to find out what is wrong.
If you go for different bikes, try at least to have similar kind of speed capacity on both. If only for the sake of your marriage!
I have met enough couples travelling, her in the little bike, trailing way behind, him in the big bike, her dropping the bike and waiting for hours… Him angry because the wifey is so slow, her angry cause the husband is always too fast and she cannot keep up…. Both seething…

not good!
Good luck on your search!