Here are a few sims of myself shifting my stats out of parry (i run a full parry setup as standard)
normal me: 339481 dps, 57181 dtps, 7547.5 TMI, 12.5 RPS, SBuptime 65.06%
10K Crit from parry: 340270 dps, 69603 dtps, 28391.9 TMI 12.1 RPS, SBuptime 61.95%
10K Mastery from parry: 297999 dps, 58934 dtps, 5346.9 TMI 12.2 RPS, SBuptime 66.11%
Results show that their is a 0.3% dps increase if one prefers Crit over parry, but this also leads to a fourfold increase in TMI. Putting the 10k form mastery into parry drops the DPS by 12%, but drops the TMI by almost a third
The RPS results clearly show that any build will have sufficent rage to attain maximum shield block uptime, and have nigh equal amounts amounts of excess rage to burn, which directly contradicts Icy-Veins's stament that stacking Mastery "will cause you to struggle to maintain high shile block uptimes" The results would indicate that if the mastery build struggles for shoield block uptime the crit build would struggle slightly more and the parry build would struggle slightly less. In fact if directly look at the Sb uptimes we can see that the Mastery build manages to have the highest uptime
I would suggest this is probably becuase Mastery has the lest spikes and they tend to be smaller in magnitude, and thus do not trigger the "ohshiti'mgonnaDIE!!" Sbar response which is much more disruptive to using SBlock on CD than 0.1RPS difference, which eqautes to 1 more Sbar every 10 minutes.
My own expierience in 5.0 in 463 blues when SS was 15 rage and Rev 10, is that attaining maximum Sblock uptime is possible with just capping hit and exp, if you never press Sbar.
EDIT: and just for fun here's me if i just straight up lose 10k parry rating and tell it to never use Sbar, just use SBlock on CD and never worry about if i cap rage
Losing 10k parry: 300158 dps, 116868 dtps, 1908.3k TMI, 7.1 RPS, SBuptime 68.22%
That's a perfectly respectable SB uptime to me.
To tag onto Agg's comment, Crit builds are when you need to tank and your Arms/Fury gear is a higher Ilvl than your prot gear.