The Nokia N9 looked like if it was running on windows 7: over 280MB of updates. Twice.
Hopefully I’m on the most recent version now and, yes, email synch seems to be faster that when unboxed as promised by the update description.

The upgrade of the DS411Slim doesn’t look like has fixed my issues with slow transfer rate from the encrypted volume.
Even worse: I’ve had the time to test with the regular volumes and it looks like they are slow too.
I’ll post more detail on my findings once I’m done with the backup od the encrypted volume and can remove it from the NAS.

The FVS336G was working stable (with the exception of a relevant slowness in managing the WAN interface up-down-up transitions) before the upgrade and seems stable now too.
I decided to give a try at the updated FW (3.0.8.12) : the list of fixed problems in this release was impressing and I was on an 18 months old version (3.0.7-24)