Hello. This is a really old thread, but since it is pretty much the only source for SP mic owners, I'll share.
Just for the fun of it, I just replaced the gate cap on my SP B1 with two polystyrene 510pF's, since I have a bunch of them. First it was really hard to tell the difference since I also had to change the preamp to another of the same kind that does have just a bit smoother sound (do not unplug a mic when the phantom is on!!). I actually changed the caps back. I then realized that I also had sung a bit more quiet in the evening after the mod, and started to hear the difference after making many sound clips.
First I thought that the sound only went darker a bit, but soon found that the originally slightly sharp low-treble had smoothened out, and perhaps even got replaced with a higher treble openness.
The midrange and overall sound is exactly as written earlier on this thread, more "open". The clips before the mod started to sound tight and squeezed in a bad way, where the clips after the mod are a bit more natural, transparent and relaxed.
B1 has it's own nature, that is almost a bit to the direction of an SM57, and that quality is diminished a bit. So, whoever likes that nature of the B1, might not like this mod. And I really need to emphasize, I don't think I would've noticed if someone secretly modded the mic, the difference is _small_. And I will never quite know how it will affect other sound sources than my own voice.
-Aki.