Seems everyone here agrees with the test of the B100 in Stereophile, in the test he found little difference in the sound adding a 4B SST to the B100. I seem to recall he mentioned maybe a slight increase in deep bass slam.
Anyway, like patrickm said, the room is the biggest concern here, do you have a big room the speakers must energize, then you might need a bigger amp, otherwise not. Of course there is a difference between what one might want, or need, if I had the money and the space for it I would probably also buy a 4B SST, but for me that would be total overkill I think.