When I hear middleweight I still think 650 single and 150kg 
The mention of pillion is the primary parameter to consider, most smaller bikes are not pillion friendly.
My advice would be to go ride the bikes on your shopping list with pillion, she will tell you real quick if it works or not. Factors not important for the rider can completely change the pillion experience. This would include seat comfort, seat height relative to rider, screen size etc.
To illustrate my point, my wife loves to pillion on a 1200 GS bit less so on the GSA. The relative seat height on the GSA means she stares into the back of my head while on the 1200 she could see over me. Surprisingly, she hates the 1600 GTL because the seat is too high which means she experiences severe wind buffeting at higher speeds.
This would be different from person to person based on their preference, height etc.