There is a difference between the sst and st. SST has smoother airy highs and better bass control. Here is my test readings for the 3B-SST and for comparison 2B-LP.
3B-SST 2B-LP
THD- Left, Right 8 ohms
20 hz- .00121, .00160 20 hz- .00472, .00460
200 hz- .00121, .00144 200 hz- .00288, .00293
2K hz- .00154, .00156 2K hz- .00296, .00301
20K hz- .00429, ..00406 20K hz- .00565, .00528
IM
.00297, .00127 .00175, .00262