The price difference for a used 3B-SST vs. a used 4B-SST is not large, and my long-term experience with Vandy speakers (any model) is that they perform better with more power rather than less. Therefore, I'd recommend the 4B-SST.
I am using a 4B-ST with my Vandy 3A Sig's, and intend to use it (or a 4B-SST) when I upgrade in the near future to the Vandy 5A's.
I am using a 4B-ST with my Vandy 3A Sig's, and intend to use it (or a 4B-SST) when I upgrade in the near future to the Vandy 5A's.