It should be sufficient enough as long as your Apple ID and iCloud account is secured with strong passcode.
Question od security is always questionable and you can see number of stolen passwords and accounts around the world, you can also find it on the Apple side. It greatly depends on your internet behave and knowledge of the internet threats.
Maybe you should consider of purchasing 1Password and probably you will get more advices from other members regarding security of the keychain.
I agree that Keychain is often sufficient for usage. That said, I use 1Password, and I absolutely swear by it. It is one of my favorite Apps, and I feel it is easy to use, made by a very trustworthy group of cryptographers, and still carries the touch of person-to-person customer support when I have an issue or question. It's cross compatibility with other types of devices is also stellar.