That is incorrect. The 8% more crit is functionally equivalent to an 8% increase in crit rate and it applies to your entire crit rate even the portion that comes from the crit buff intellect and the 2-set. Mathematically for throughput it is indistinguishable to a crit rate increase. So that also needs to be factored in for determining where you are.

If you have 42% buffed crit and the 2set, which adds about 6% and the crit buff for another 5% and the amp trinket at 8%, you are looking at 57.24% crit

Using the balance point for aegis generation: crit = (1+mastery)*(1+0.5*mastery)/(2.4+1.6*mastery)

You are going to need 52% buffed mastery at the very least otherwise you are going to be losing not only healing but also aegis. In your BIS set you will have 49+8 = 57% mastery

Here is how aegis changes with crit at 57% mastery

Code:

0.4 0.80698
0.41 0.8271545 0.0201745
0.42 0.847329 0.0201745
0.43 0.8675035 0.0201745
0.44 0.887678 0.0201745
0.45 0.9078525 0.0201745
0.46 0.928027 0.0201745
0.47 0.9482015 0.0201745
0.48 0.968376 0.0201745
0.49 0.9885505 0.0201745
0.5 1.008725 0.0201745
0.51 1.0288995 0.0201745
0.52 1.049074 0.0201745
0.53 1.0692485 0.0201745
0.54 1.089423 0.0201745

The first column is crit in 1% increments, the 2nd column is aegis and the 3rd column is the absolute increase in aegis

This is the equivalent increase in aegis (ignoring the healing buff completely) with mastery at 57% crit

Code:

0.4 0.9576
0.416 0.97500096 0.01740096
0.432 0.99254784 0.01754688
0.448 1.01024064 0.0176928
0.464 1.02807936 0.01783872
0.48 1.046064 0.01798464
0.496 1.06419456 0.01813056
0.512 1.08247104 0.01827648
0.528 1.10089344 0.0184224
0.544 1.11946176 0.01856832
0.56 1.138176 0.01871424
0.576 1.15703616 0.01886016
0.592 1.17604224 0.01900608
0.608 1.19519424 0.019152
0.624 149216 0.019297.21492

Same as before but mastery now increases in 1.6% increments.

As you can see at these high levels of crit and mastery the two stats are exactly interchangeable in terms of just aegis. You can switch around quite a bit of mastery for crit with a minute reduction in aegis, but a large change in the + healing bonus.

As I said you have to be quite careful about stacking crit. You can just sacrifice a non trivial amount of + healing for absolutely no benefit other than more DPS at the level of 0.05 to 0.1% of total DPS.

For example if you are at 42% crit and 57% mastery and you choose to go to 47% crit and 49% mastery. On the face of it, it looks like you are trading 4% healing for 2.8% aegis, but in fact its not, because the 2 set adds 5-10% more crit depending on the spell.

With 5% more crit you are trading 4% healing for 1.7% more aegis aegis, with 10% more crit, you are trading 4% healing for 0.7% more aegis. If you add the amp trinket its even more slanted.

IMHO your BIS has too much crit.