Hi, here is my first try, use X-Particles generate Thinking Particles then cached into .bin file and reload.
nice test!
…now do the following:
a. increase the particle count 100 times
b. make the “Final Pass Exponent” two digits larger (if it was -2 make it -4)
c. Turn on “Use Lighting Pass Density”
d. Make the exponent for “Lighting Pass Density” large as well (-4 -5)
Render again 
Nice renders! Thanks for sharing ihdt.
Definitely increasing the particle count should smooth the grainy look. Krakatoa can handle the extra particles (: