Buff of weapon and stat bonus

Good morning fellow gamers.
I am the happy owner of a wonderful +5 Great sword of Artorias and i was wondering if there was any way to magicaly buff it. When i try to cast magic weapon on Sun blade, it does not work. Why is that ?

The second question of the day : Is there a site where i can see the bonus given by a given stat ? For example, an "S" bonus with 99 strenght ? How much damages would it add ?

Have a nice day.

This type of info is available in the Wiki if you care to read up on it there.

You can't buff many types of weapons, including magic (enchanted/divine/occult) and elemental weapons.

You need to read up on stats, stat bonuses and how the damage in the game works on the Wiki as no one will bother repeating all of it here. But suffice to say there's some serious diminishing returns at play especially after 50 so 99 strength is not going to be 'worth' the extra 49 soul levels.

If you want to see what your build will be without actually making it use mugenmonkey.com/darksouls/