The data is a little noisy, but it’s pretty clear that the value of expertise drops off pretty steadily up to around 9%. From the bottom graph, we see that 9% is where we hit the 6.667 rage threshold, and correspondingly we see a “knee” in the Shield Block uptime curve. Shield Block’s uptime is saturating to it’s asymptotic value of 66.67%, and this “knee” is where we start really feeling the effects of that cap. Since warrior skills are equally affected by hit or expertise, we can surmise that hit behaves similarly, and what really matters is that the sum of hit and expertise is 9% (though of course, hit over the 7.5% cap doesn’t count!).
Beyond the 9% threshold, SB uptime only increases slowly and the value of hit or expertise is primarily due to the smoothing of rage droughts that I described earlier. The bulk of the rage generation beyond this point is what we consider “wasted” in this simulation (more on that in a second). So we can reasonably say that any hit or expertise beyond a total of 9% (i.e., hit+expertise=9%) has little to no effect on Shield Block uptime
However, we can come up with a conceptual estimate based on the assumption that all of the “wasted” rage can be converted to Shield Barrier casts. There would obviously be a little attrition, in that you might push Shield Block back a few seconds if you use a 60-point Shield Barrier at the wrong time, but overall the result shouldn’t be that far off from the approximation. Even in our near-capped case, where we “wasted” 362 thousand rage (which is about 1.8% of all rage generated), that’s still only an extra Shield Barrier every ~5000 seconds, or every ~83 minutes.
We can do the same analysis using our expertise scaling data. At 14% expertise we’re generating 6.983 rage per second. If we assume that everything over the 6.667 RPS we need to maintain Shield Block gets turned into Shield Barriers, that’s 0.316 rage per second, or another Shield Barrier every ~190 seconds (about every 3 minutes). So that extra 6% expertise beyond the 9% threshold buys one Shield Barrier every fight, maybe two on a 6+ minute encounter. That’s doesn’t seem like a lot of survivability for a 2040 rating investment (then again, it only takes one sometimes…).