Synology DS411Slim and encryption: DSM 4.0 not helping performance for me

I’ve written recently about the poor performance writing to and reading from an encrypted volume on my Synology DS411Slim.
In an attempt to improve the bad numbers I’ve decided to take the risk of updating from a firmware that I knew was working for me (DSM 3.2) to a more recent one (4.0)

The interface looks sleeker than the previous one, but unfortunately there it is no improvement at all in writing to the encrypted volume.

DSM 4.1 is available too, I’ll likely give a try at it too as there are no major reports of problems.