http://vg.curse.com/database/items/details/1209058/
So i examined the item tonight "Flawless Pariah's Jagged Tunic of the Marked" which has 177 crit chance on a few alts

Vs lvl 47 = 5.88%
Vs lvl 49 = 5.13%
Vs lvl 50 = 4.78%

From a simple equation, comparing the vs 50 and the vs 47, you can get a constant number to be used for extrapolation
4.78 / 5.88 = 0.8129                 (you also get this if you compare vs50 to vs49 and cube it - proof the equation is linear)

So if we put this number back in we can work out what the % crit is vs a lvl 53:
4.78 * 0.8129 = 3.89
Therefore the 177 crit chance is :-

Vs lvl 53 = 3.89%

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So...assuming the crit chance of most abilities can never exceed 40%
for APW (level 53s):-
40 / 0.8129 = 49.21%

You need a total of 49% crit (vs lvl 50) to be capped for Raiding

Yea likewise tanks would need:
65 / 0.8129 = 79.96% mit to be capped for Raiding