Whiterams experience with the CS is pretty consistent with mine and the general consensus - its a bright, tight pickup. Clear and punchy rather than heavy or grindy or anything tremendously overtly metal. That does make it a great pickup for detuning, and I've had it down in drop A# on 24.5 scale and its still been tight and clear.
I've also tested an uaberschall with one of my guitars that had a C-pig, and I thought it was muddy, so that adds up qualitatively.
The C-Bomb is one of my go to pickups for detuned metal. Its extremely tight, quite smooth but not overly so and pretty even across the range, with a bit of a mid hump, but nothing major. I too had little luck detuning the standard nailbomb significantly, and feel that for my tastes it bottoms out at about C/drop C. However, my tastes are for extreme tightness and precision, which those bands arent. The style youre after, to my ears, requires a more organic character and benefits from a little looseness, so I think the A-Bomb would do fine, and the C-Bomb would be too clinical. (Though it is rather unclinical in character for such a precise pickup, I think its a bridge too far for the post-rock/post-metal style). Certainly it retains little to none of the 'vintage' character of the nailbomb (which is very much a metal pickup with a vintage organic vibe to it), or the cold sweat, which is basically an underwound ceramic nailbomb, or so I'm led to believe, and is more organic and quite a bit more toppy and middy with a more open, less compressed style, but I dont think it will give the low end density and impact that you want for those bands.
The painkiller would be OK in some regards and horrible in others. Its got a big grinding midrange and uncompressed dynamic response that would fit the styles of tone of the bands you mention well, but its also got an overly tight low end and a really sharp, almost clicky attack in the top end that doesnt fit the vibe of those styles well. I'd say you want a clear but rounder attack, not a hyper-precise ice pick.
/Thesis.