Bryston 4b or 3b SST

New poster, long time lurker in these forums...

I have a pair of Maggie 3.3rs (4 ohms) and I love their sound. I power them with various mid-fi amps I have, including a Counterpoint NPS-200 and a McIntosh 2105. The sound is very pleasing however I frequently wonder if the sheer addition of more (quality) watts per channel would enhance my experience. At least when I want to listen LOUDLY as I am about to do on this fine Friday afternoon...

I have a limited budget (at least after I found out my car needed new brakes yesterday) and so I am looking at two relatively similarly priced amps up for sale - the Bryston 3b SST and the Bryston 4b.

I'd like to ask those with experience with these two amps which would be the most likely to sound like a noticeable upgrade to my current amps, if either.

I expect the 3b SST is much more refined. However its power rating isn't a ton higher than the amps I have (and I consider the Counterpoint to be fairly refined, other than it doesn't push the speakers quite like the Mac). The 4b seems to offer the power/current necessary to be a substantial increase in power, but if it's less refined would it really be better than the 3b SST pushed to the upper end of its comfort zone?

All opinions appreciated. What I really want is a Levinson 23 but unless it comes with pads and rotors for my car, I don't have that budget right now.