You don't have to max Shield Defense to get a lot of defense out of a good sword and board set-up. Each point after the first is less efficient anyway.
Technically, each point of Shield is MORE efficient than the last.
Going from 50 block to 55 block reduces incoming damage to 90% of what it used to be (on average).
Going from 55 block to 60 block reduces incoming damage to 88% of what it used to be (on average).
The only reason to STOP stacking block is that at a certain point you don't
need any more survivability.
