I have a 1000 and can't personally speak to how a 650 would handle, but from what i gather on here if you plan on touring 2 up, go 1000. It handles my wife and I great, plenty of power. I thought i also read brakes and suspension were better, again better for 2-up.
Im a little confused that you have an HD RK, but wife doesnt want to downsize and your looking at a Wee, or even a Vee. You're not going to match the comfort for the passenger, its like sitting on a couch vs a table chair. That might be extreme, but you get the idea.
I attached a picture of the Givi V47, perfect size for me. Could hold two full face helmets for reference. We were out his past weekend and decided to do some light grocery shopping. Two of us, case full of groceries, all good.
2016 DL1000 ABS