Thanks for your quick reply. I did it and it works flawlesly.
I folowed this guide :
http://community.wd.com/t5/WD-My-Cloud/GUIDE-Transmission-2-82/td-p/619597/page/10
My speeds are back to 45-50 megs and the dashboard is quite responsive.
Of course I was hoping for a quick fix from WD , like a resigned v3 FW, but my lesson is learned here :NEVER TRUST WD SOFTWARE UPDATES !!!