I reckon I should speak up since the priming powder testing mentioned above was mine. The testing included 20 trials each of Swiss Null B, Swiss 4f, two samples of Goex 4f, Goex 3f and 2f. There is definitely a difference in priming powders. Please read the article for the rest of the story, but let me start you off with this:
The fastest 3f trial (among 20) was slower than the slowest time recorded for Swiss Null B.
Human senses are terrible tools to determine priming powder speeds. I believe if you can hear a difference, the delay was caused by something else - like fouling, poor flint edge, lock management, etc. (I realize this puts me out on a limb.)
Regards,
Pletch