Is there any benefit to have charisma over 10? Or do you make all charisma checks if you have 10?

Better bartering prices, although you only need a Charisma of 8 to hit the cap with all relevant perks.

Gives your companions more health and damage, gives you better prices, and probably (don't know) gives a higher chance to passify enemies.

Idk about the pacify thing - when I'm out of power armor and drink a beer I'm at like 16 or 17 charisma and I'd say the pacify rate is still maybe 10%

I have a 0% success rate on ghouls or super mutants (idk if it's even possible, but it gives me the option).

Yes wasteland whisperer, I always end up with an army of gouls and synths (apparently aren't robots) fighting for me.

I must be the least lucky person ever then because I've never gotten it to work - only on like 3 dogs ever. I have all the perks, they just don't do anything for me.

Also, when I try it, the little icon shows up, then sometime it'll instantly tell me it failed or other times it's delayed like 10+ seconds.

No I cannot for the life of me get it to work on raiders for some reason, super mutants with bombs I can do though assuming dogmeat doesn't bite them 2 seconds later, I really need to send him to the pound. Just luck of the draw

There's plenty of clothing one can come by that will boost charisma tremendously

Im constantly in power armor, when I want to barter out pops a guy in a suit

I have had 10 Charisma since Level 4 and I have failed one speech challenge, it was after I hit 10. I push everyone for as many caps as I can get for each job and when I pushed Hancock to the max he told me I could take the basic 200 caps or forget about it. Made me respect him more!