Edit: ok. forget the last couple of posts, had the wrong mastery to block conversion :-/
Edit2: found an error in the Vengeance AP.. we are getting closer :-)
Updated results:
block on CD + barrier for the extra rage
Simulationcraft Results
barrier on CD (without overwriting itself)
Simulationcraft Results
Now, barrier is only a little bit better than block. Feel free to point me to simulation errors.
Napkin math for Shield Block value agrees:
We are avoiding 20%, thus 80% are rolled against block:
w/o SBlock:
We have 30% block with a ~65% critical block chance. of those 30%*65% = 19.5% are critical blocks and reduced by 60% and 30%*(1-65%) 10.5% are normal blocks and reduced by 30%: This means the 80% are reduced by 19.5%*0.6 + 10.5%*0.3 = 0.1485%
with SBlock
We have 100% block with a ~65% critical block chance. of those 65% = 65% are critical blocks and reduced by 60% and (1-65%) =35% are normal blocks and reduced by 30%: This means the 80% are reduced by 65%*0.6 + 35%*0.3 = 0.495%.
Using SBlock therefore reduces our damage taken by 0.495 - 0.1485=, but only the 80% that are actually hit, so all in all, it is a reduction of 27,72%. As we are getting three hits over the 6 seconds, a button push of Shield Block reduces damage taken by 83.16% of a white hit(close but less than Shield Barrier's 100%).
TLDR, Shield Block looks a bit weaker than Shield Barrier.