I've currently got 10 Agility, but I'm wearing a hat which gives +1 Agility, so I've actually got 11 Agility. Is this correct, or is 10 the absolute max meaning the hat won't make a difference?

Thanks guys.

10 is max.

You may go over 10, the game will not show it. However, anything over 10 is doing no good.
Now, if I am not mistaken this does not affect luck and finesse. you can have luck 10 and take the perk and still get the 5% crit, in total make it 15%. I think this is because it adds luck equal to 5 (or 5%) to crit.

So seeing as I'm already at 10 Agility, I guess there's no need for me to wear the hat (which gives +1 Agil) as it won't increase my agility anymore?

right, its doing nothing, unless you like how it looks.

For example, if a person had 8 STR, and got the implant, (+1) drank a beer (+1) and took buff out (+2) you would have 12 STR. BUT the game will not show it, not will it adjust anything past 10. SO you wasted a buff out.

Same with agility, if you already have 10, that hat is doing nothing, its just there for looks.

if the hat has no/very low DT then yes

Much appreciated guys, thank you very much.

DT is way better than an extra agility point anyway. Even if you had 9 agility, you should only be wearing the hat because you like how it looks. You can get helmets very early on in the game. Personally, I wear a bandanna that has 0 DT and +1 perception simply because it looks awesome with sunglasses and combat armor.

I don't think it will go over 10.