Am I reading it correctly?
The specs (THD, S/N, etc) for the 4B3 (and 14B3) are not that much off those for the 4B2 (and 14B2). Miniscule by human auditory threshold levels, in fact.
This is a big reason why I stayed with my 14B2.
Also, the reviews for the 4B3 amps all are consistent on at least one major improvement: noise is reduced, compared to other amps, incl the squared series. Well, I already have a subterranean noise floor: my amps are plugged into Triton + Typhon power distributors (Shunyata), which were game-changers for my system (I have dirty power lines in tall condo bldg). So it's a futile uphill battle for my system to get even quieter in an audibly substantial way.