VNC quality in Mavericks

Hi there,

we have a MacMini (Server installed) connected to our fiber optics internet connection (100Mbps) over a public IP address. We always used it to control the MacPros connected to the LAN (e.g. during the rendering) when we're away.

It has always worked perfectly because the LAN is dual Gigabit and the WAN connection is stunning fast.

Yesterday the internal MacMini's HDD (with 10.7.5) died and today I replaced it with a Samsung SSD with a brand new Mavericks installation.

Everything went fine, the server is running again with all the services, exactly like before.

There is only one (big actually) issue: the VNC screensharing quality. It's awful. You may say it's due to the WAN connection, but it's not (look ad the Speedtest)

And to enforce this also in LAN VNC connections to the server and viceversa the quality has dramatically dropped down: very high image compression and very slugghish behavior.

I tryed setting High quality in Screen Sharing App, the result is - better in terms of quality - but totally unusable in terms of response.

And it wasn't before!

I also tryed this in Terminal with no results.

defaults write com.apple.ScreenSharing controlObserveQuality 5

Is there any way to control the VNC quality/bandwith?

Thanks in advance.

Piero.