B&W 801N and Bryston match

I have a pair of B&W 801N as part of a home theater system and I'm looking to upgrade my amplifiers. I like Bryston because of their warrenty and pricing on the used market. If you had a choice between upagrading the amp to run the 801N only would you choose the Bryston 4B SST or the Bryston 7B ST. I know I would be sacrificing some power going to the 4B SST but would the benefits of the SST line be worth it?
Sacman this is the information I was looking for. I know you ended up with the Krells but how did the others do in comparison? What differences did you hear between the amps?

I love B&W midrange and tweeter but for my music taste demand speakers with decent low end bass. We got the B&W 801N for its sub and no amp could drive them properly. We tried the Pass Labs Monos and it sounded really awesome but the speakers clips the amps in some occasions. All others sound really underpowered. I like the transparency, details and bass from the Krell and the CAL MCA2500 the most.

They're very hard to drive I take it. What does the impedance dip down to on those?