Considering that most TC 5 Speed machines will run out faster in 4th than in high gear, you would think that a 5 speed would be enough. I felt that way until I went riding out west in ’06 with a group of folks that had Cruise Drive machines. The first thing that I did when I returned home was to stuff a 6 speed in my ’02, 113” FLTR.
Of course the machine must have the torque to pull 6th gear, or it simply doesn’t make sense to consider. As you know, taller gearing with descent torque has a substantial impact on comfort when cruising at high speed. Based on my experience riding with my Wife and her machine, when she is happy I am happy; when she is comfortable, I am comfortable. It’s amazing how much impact the machine running next to you has on your riding experience.
If you like to run fast and mamma’s machine is more comfortable to ride at high speed, you will be more comfortable running at high speed. When momma is comfortable, SSB will be comfortable. Of course the reverse almost always true; at least for me it’s true. It may be kind of selfish, but go ahead and get momma one for your riding pleasure.

Also, as you describe the benefits of the heavy duty transmission, it might not be a bad idea to occasionally mention that this is a Motorcycle transmission....stopping now before this gets too personal.

Good luck.