From your first list I really like [name]Clark[/name] and [name]Everett[/name] and from your second list I really like [name]Miles[/name] and [name]Rhett[/name]. I have no concerns about [name]Hugh[/name] or [name]Vaughn[/name], also, I just happen to like the sound somewhat less, personally.
Here are some thoughts.
[name]Breck[/name] - it’s great Breckenridge has such meaning to you and you want to connect him to that. However, I agree with a pp that it sounds like a shampoo, it also kind of sounds like wreck, eck, bleck, etc. I also just think it’s uncommon enough that it’ll be heard wrong - people will hear [name]Rick[/name], [name]Brock[/name], [name]Beck[/name], [name]Brick[/name], etc. [name]Grant[/name] and [name]Nolan[/name] are pretty recognizable in comparison and I think it might be an unfair balance. Finally, his initials would be BM - hardly the worst, there are plenty of people with those initials so obviously it’s fine, but I know it would bother me, at least. I think this could be a great middle name, and in the middle spot you could even go with full out Breckenridge, perhaps. Or [name]Ridge[/name]? I wouldn’t recommend [name]Ridge[/name] in the first spot because everyone will hear [name]Rich[/name], but [name]Ridge[/name] is pretty cool otherwise. There’s also the Irish name [name]Breccan[/name], which I like a bit better than just [name]Breck[/name].
[name]Clark[/name] - I don’t know the Griswold reference, will have to look up. It just makes me think of [name]Lewis[/name] and [name]Clark[/name] and of [name]Clark[/name] [name]Kent[/name], and of [name]Clark[/name] [name]Gable[/name], and those are mostly neutral/positive. It’s also a family name for me. It’s surname-y like [name]Grant[/name] and maybe even [name]Nolan[/name], and it seems like a one-syllable first name would be nice with your longer surname. I think it’s a good choice.
[name]Everett[/name] - this name is so handsome and I love it on its own or with nickname Rett/[name]Rhett[/name]. I think it would be a solid fit with [name]Grant[/name] and [name]Nolan[/name]. There’d be a subtle theme going on, first child = 1 syllable, 2nd child = 2 syllables, 3rd child = 3 syllables. If you plan on more it might be hard to keep that up, although not impossible, and certainly not even necessary : D.
[name]Hugh[/name] - a perfectly solid choice, again, a one syllable name is probably good with your longer surname (though I don’t think [name]Everett[/name] is too long).
[name]Miles[/name] - again with the one syllable thing, and, I think alliteration with M names is particularly pleasing, so you may want to consider that. This might be a really memorable name!
[name]Rhett[/name] - a perfectly handsome choice, although I do think it might be somewhat hard for people to hear, like [name]Breck[/name]. Slightly more expected than [name]Breck[/name] though, so that could help. What about [name]Brett[/name]? I think it continues to have some of the same concerns, but again, less so.
[name]Pierce[/name] - I like this name fine, but find it has a somewhat pretentious air to it and if your husband also has reservations it’s easy enough to let it go.
[name]Drake[/name] - similar concerns to [name]Pierce[/name] and now with the rapper so popular I’m sure you’d get “oh, like the rapper?” all the time.
[name]Vaughn[/name] - similar thoughts to [name]Hugh[/name] : D.
Good luck!