Hi,
I can't really comment on the difference in sound between the two because I only own a 4BSST2 and I have never listened to an SST.
But here in Canada, the difference in price between generation of 4B is ruffly about 1K$ CAN.
4B - Sub 1K
4BST - about 1.5K
4BSST - about 2.5K
4BSST2 - about 3.5K
(Source = mainly "Canuck Audio Mart".)
Give or take a few hundreds depending on general conditions, remaining warranty, etc.
Take care!