i'm gonna agree I myself am gonna try out the hit/exp cap then pure mastery gems after.7-8 Rs misses is a lot of potential extra runes and rp gain from them for more runes and more rp gen, the cycles repeats.
Nothing was said about a GCD 'cap' learn to read (and get a better grasp of the English language whilst you're at it). All that was said was that a missed ability = a loss of a GCD which means more rp loss = rune loss, white hit loss also accounts for more loss of rp and therefore runes.
No Dk tank even if reforged out of hit/exp will have 0 rating, you yourself said you have around 3% hit 4% expertise, or something like that.
I looked on WoL on 10 normal and HC in the top 20 and no log with a dk and pally tank was to be seen around the rank you claimed to be at, provide some evidence so we can check your logs to back up your claims. Be it if you were in the 25 man bracket which I didn't check.
The difference of caps can be substantial dps gain with only minor increase in dmg taken.
As an example, say a boss has 238 mill hp, thats 2.38 mill dmg lost which is around ~5k dps loss over 8 mins. Blade lord on hc 10 has aorund 195 mill iirc, and even that is far more than the 450k bullshit you pulled out of your arse earlier let alone the ~8k dps you mentioned... I've seen a fair few wipes with less hp left than that, not to mention that this example would require a fight to have linear non fluctuating dps, i.e. 0 dmg increase debuffs on boss via a mechanic/burn phase.
If you lost the hits during a burst phase with all cds up, that dps loss would be even more considerable.
I suggest you think about your own perception of class knowledge or even just your math, as you've just been told your math is shit by 3 ppl, 1 of which theorycrafts and has the highest raid experience possible over this content.