Bridging amps vs single amp of same power

I recently picked up a bryston 3b which is slightly underpowered for my speakers.I can pick up another and get 200w ea in mono,or go for a 4B which would be 200w/channel.Is one better then the other.Price would be a little more for the pair of 3b's.I'll be driving thiel cs3.5's.
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I've heard that the 4Bst is significantly better than the 4b, and the 4Bsst is one further step better. Just in case you can swing it. All the Best, Peter