This was just a quick, unscientific "it's late at night but I can't wait any longer and need to know how good it is" test, but since the results are more than promising, we thought we should share them with you.
Test setup:
* Apple 2020 MacBook Pro M1
* Reaper, native Silicon beta
* 48kHz, buffer size 512 samples
* Diva 1.4.4, rev. 9709 (no ARM support), running bridged via Rosetta2
* "BS Deep Space Diva" preset (accuracy: great), playing six voices
We simply duplicated the track again and again, until the CPU bellyflopped.
And to have something to compare it to, we did the same test on an old, trustworthy MacBook Pro from 2015 with a 2.2GHz Intel i7 (this is starting to feel a bit like on an episode of Mythbusters).
Results:
Multicore option in Diva disabled:
On the 2015 Intel MBP, 3 instances with 18 voices ran without glitches. The fourth instance already produced too many dropouts to continue working.
On the 2020 M1 MBP, 20 instances with 120 voices ran glitch free. With one more instance and 126 voices, there were some dropouts, and it finally glitched heavily when adding instance 22.

Our jaws dropped collectively at that moment.
With Diva's multicore option enabled in each instance:
On the 2015 Intel MBP, six instances with 36 voices ran glitch free, a seventh instance produced occasional dropouts, and the eighth instance brought it to its knees.
On the 2020 M1 MBP, only five instances with 30 voices played without glitches, the sixth instance already produced heavy crackling.
This is not exactly the result we were hoping for, but we are still in the process of porting our plugins to run natively (i.e. without Rosetta2) on the new Silicon chips, and we expect to see some better numbers by then.
Otoh this first test indicates that on those amazing new chips, there seems to be way less need for a multicore option than on traditional Intel chips.
I'm sure we will conduct way more tests, but right now we are simply elated and relieved to see our plugins performing so incredibly well under Rosetta2.
Rest assured, after these initial results, we are more motivated than ever to port our plugins to the new Silicon platform. Please be patient, though. The porting will still take quite some time, as it turns out to be more complex than anticipated.
Update December 8:
We now have a first version running natively on the M1 (i.e. without using Rosetta2).
With this version, we ran the same test project again, and could now run up to 32 instances of Diva with 192 voices without dropouts.
A word of caution about those numbers: This was just a very simple lab test, running the same preset, playing the same notes in each instance.
It remains to be seen how the plugins actually perform in real world projects.
We also have a hunch about the weak performance when using Diva's multicore switch, and we hope to improve this over the next weeks.
Cheers,
Tas