[name]Beckett[/name] - 5, love this name and the nickname [name]Beck[/name] or Becks, I think it will grow up well but is cute for a little boy too.
[name]Griffin[/name] - 5 - my little brother is named [name]Griffin[/name] (23) and he loves his name. When he was little we called him [name]Griffy[/name], then [name]Griff[/name] or [name]Griffin[/name] once he was older. You could also use [name]Finn[/name] as a nickname.
[name]Brant[/name] - 2- my DH name is [name]Brent[/name] and he HATES his name and people always confuse [name]Brent[/name]/[name]Brant[/name] and it jsut sounds blah to me.
[name]Weston[/name] - 3 - this is cute but for some reason i can’t picture a grown up [name]Weston[/name], but can I can see a grown [name]West[/name], maybe just [name]West[/name] by itself?
[name]Cole[/name] - 3 - not really my style but it is cute, i picture a little blonde kid with this name.
[name]Corbin[/name] - 4 - distinguished and uncommon but there really are no nickname possiblies, maybe [name]Gavin[/name]?
[name]Mason[/name] - 4- does sound like your LN but I still love this name no matter how popular it gets - every [name]Mason[/name] I have known is so cute…i went to undergrad w/ a couple Masons that were very attractive so maybe that is why i like it so much 
[name]Clayton[/name] - 1 - all i think of is [name]Clay[/name] [name]Aiken[/name]…sorry.
[name]Donovan[/name] -3 - an ok name but I HATE the nickname [name]Don[/name], reminds me of an old man, maybe you could use [name]Van[/name]?
[name]Kean[/name] - 4- i like this just not sure I am saying it correctly, [name]KEEN[/name]…it is different, easy to spell and sounds good w/ your last name
[name]Trey[/name] (as a nn for a III) - 3, okay nothing special but i dont hate it
[name]Reuben[/name] - 1, not my style at all, i just picture a fat dirty man or a fat kid playing on the playground by himself…
Clarkson - 3, i think 5 for middle name, i think it is totally usable and [name]Clark[/name] is kind of refreshing and something you don’t hear very often
[name]Bennet[/name] - 5- spelled [name]Bennett[/name], i think it is classic, easy to pronounce and spell and would fit him through life.
a few suggestions
[name]Kellen[/name]
[name]Kelton[/name]
[name]Owen[/name]
[name]Cooper[/name]
[name]Anderson[/name]
[name]Tate[/name]
[name]Channing[/name]
[name]Cannon[/name]
[name]Rafferty[/name]
good luck!