@david_ten
I have no experience with 211 or 845 amps, but I would speculate that in **some** cases an explanation of why **some** of those amps may sound "slow and boring" compared to 300B amps derives from something Ralph ( @atmasphere ) has pointed out in the past.
What he has pointed out (and it makes perfect sense to me) is that since the distortion produced by a 300B (or other low powered SET amp) rises dramatically as output power becomes a significant fraction of its capability, while also becoming vanishingly small at low power levels, and since our hearing mechanisms use certain harmonic distortion components as loudness cues, from a subjective standpoint such amps will tend to have a greater perceived contrast between high volume peaks and softer notes.
In other words, dynamics will seem to be enhanced relative to the presentation of many other kinds of amps.
While if everything else is equal (including speaker efficiency and listening volume) that effect will occur to a much smaller degree, if at all, with a more powerful 211 or 845 SET amp, since the amp will be operating at a relatively small fraction of its power capability even on high volume peaks.
Best,
-- Al