ok my take,,(and agree with alot already said),,,Sid, would not work for me, he sounds like a nice dog, but with a dog like Peyton, she would most likely end up intimidating the heck out of him, (been there done that),,and if he's a soft already,,he's gonna end up a "marshmellow" so I'd pass on him too.
The BC in the video's,,I would HIGHLY consider,,for most of the reasons you state, and my reasons would be (just from watching them interact on the videos),,he does seem to balance Peyton out, calm her for whatever reason,,they co existed quite nicely, YET, they both are not so "into" each other that it would detract from them being into "YOU"..get what I mean??? He does not appear over the top I-am-on-a-constant-mission border, (and there are some of those out there
) he had very good focus on you, vs being "into" Peyton the entire time,,they tolerated each other well.
I did notice his "growlybarky" thing at Peyton in the last video, and that was probably good for her, I liked her backed off reaction vs I'm gonna push you further.
I have lived with alot of really wonderful dogs, always had multiples, and I have to say, I would always always pick a dog who was more into "me" than my other dogs..Fortunately for me, it's always been this way. Sure they play with each other, but they are not obsessed with each other,,they are obsessed with ME, which is how I want it
) Makes for easier living and easier training..
I think the next step I would take, is see if you can take this boy for a week and see how it goes,,training him will most likely be a breeze so I'm not going to even get into that,,BC's are incredibly smart, I again, like that he isn't over the top compulsive, obsessive, and seems quite willing..
Ok, that's my 2cents
))