I believe the most you can get to is 85% damage reduction from blocking. Anything past that is wasted. I'm trying to plan how many points I will take in Shield Wall so I reach the cap when I eventually have 100 Block Skill. (is there a formula to explain how Block Skill works with Damage Reduction?).
I have also read somewhere that the tooltip for Shield Wall is bugged, and each point is actually worth 10% (so 5/5 would be 50%) is this correct?
EDIT: This is in regards to using a weapon and shield.

