Lax, fwiw here is some anecdotal info. Sorry if a little lengthy...
I had to upgrade our senior management team late last summer from 5's, and ordered a 6+ for our CEO, myself and 2 other VP's; I ordered a 6 for our CEO's Exec Admin; one other VP said she'd stay with the 5 that she had for awhile:
I went directly for the 6+ myself: I need to review spreadsheets and contracts/other documents remotely on a frequent basis, and liked the extra 'real estate' for reviewing. Found the phone a little big a first, but have gotten used to it. Don't get the comments around back pockets/etc, but I don't wear skinny jeans at work, and find it fits fine in a suit pocket, my shirt pocket, my pants front or rear pocket. Camera I found better, battery has been fantastic; resolution of the display is notably better/richer. I don't carry a personal cell phone, as I am able to use my work one for personal purposes....if I did have to carry a personal phone, I'd probably just stick with a 5. That being said, since these are work devices, the 6+ was more suitable for my needs.
Our CEO didn't really compare the two, and just took what I got for him.
Our VP Marketing had her 5 crash, so I took the 6 that was destined for the Exec Admin and gave to the Marketing VP to use while her 6+ was coming in. Originally the VP Marketing said she would stick with the 6, but she used my 6+ for awhile and decided to wanted the 6+. Again, screen resolution, size (for viewing media/etc), and battery were important to her
Our VP Creative was waiting for his phone, and considered the 6 as well, but uses his phone for a lot of video, and content rich documents; again the larger screen and better resolution won him over, as well as the battery life - especially in talk mode (since he spends much of his day on the phone)
The Executive Admin was upgrading from a shitty BlackBerry, so anything was an upgrade for her.
Finally, our VP Business Development decided to upgrade after seeing the two different phones in use, and trying each of them for a bit. She also decided on the 6+.
All 5 who got the 6+ were initially unsure about the size, but each has gotten used to it. All have been happy to have selected the 6+ over the 6.