I had a go, It is a tricky material to make because its inherently slow, achieving its lightness from the 'depths'.
I'm getting a benchmark of around 170 on my machine for the simball which is pretty slow
I think negative attenuation is the key here (I used -.4). and a very high coeff (I used 20000, it doesn't affect rendertime, assuming you compensate by making the sss darker) keeps it solid loking in thin areas. Otherwise its a basic glass with nd1.48 ... these values are just guesses though.
I was wondering why there is discussion sometimes about adjusting attenuation depending on the size of an object?, surely marble is just marble whatever size it ends up. Personally I haven't been worrying about the scale of objects when applying sss materials and that's been working so far..... so why is it mentioned?, and I've noticed its actually a function of the translucent wizard.. Is it just a convenient way to change the look without worrying about the reality?