Jm Lab-which is better?

How much better are the new Be range of speakers versus their own previous generation egMezzo utopias.Can the berylium be inserted into the previous generation speakers with ease?Are there any stark differences bet the 2 generations?
I owned the Electra 906 for about a year and liked the music coming through it very much. I just this past weekend had the 907 Be at home to audition side by side with the 927 Be's. I felt the 907 Be to be a very substantial improvement compared to the 906. On balance, I liked the 927 more. The 907 came across very well on its own terms, but I found the 927 richer, rounder and fuller through the mids as well as the bass. I note that another contributor in another thread had the opposite reaction, preferring the 907s. But I think we shared the reaction that the Be line was a significant step up. How cost effective a step is a challenging question. Lots of credible competition in those price ranges.
I also owned a pair of the 906's and recently upgraded to the 907Be models. These speakers are excellent. That tweeter is just amazing. It is very smooth and yet at the same time very detailed. Something I have never heard before. Usually it's one or the other. You can not purchase the tweeters seperately and they wouldn't work with the old Electra or Utopia series even if you could. Although I think the Mezzo's are a wonderful speaker, if you can afford the new Be series, by all means do so. I wouldn't say there is a stark differnce between the two series, as there is a common thread. However, that new tweeter is NOT a subtle difference. The Be tweeter made me forget all about my old electrostats.
Thanx for the input.
Note the favorable review of the 907 in issue 33 of
Hi Fi +, which I just picked up yesterday.
A friend of mine owned both Mezzo Utopias and then Alto Utopias BE (which were a direct replacement in JM lab line to Mezzo). He regreats selling Mezzos.

His system consists of JRDG Synergy IIi pre, JRDG power amp, Audiomeca Mephisto II CD.
I think the diva and alto be are not as good as the mezzo.