In the sonogram, the purple-blues are the loudest frequencies and the yellow-whites are the softest. As the image contests, my ears weren't fooling me - in the droning hum of the warehouse, these capsules sounded practically the same. Any subtle differences might be attributed to the different rigs (headphone, parallel boundary) that these mics were mounted in. There are some small distinctions between the mics in the low freqency range (the fat blue bands) that may indicate that the Primo and SoundPro were a little bit quieter, but if one were to really want to test the noise levels of these mics, It might be best to find an anechoic chamber.
Rob D's linear sonogram at -90dB to 24K:
click on picture to enlarge