Have had both 1800x, 2700x and now 3950x. Must say that the 3950x is the first of the 3 that feels really stable. Can now run my G.Skill 3200 mhz CL14 in the 3200 mhz they are meant for which did not go either 1800x or 2700x.
Worth noting is that I ride my almost 3 year old Asus Crosshair VI Hero, awesome by AMD that they keep the pedestal alive for so long!
I run a small game studio and doubling the number of cores means a lot. For example, I bake our smallest scene in 36 minutes instead of 53 minutes in 2700x. Will be fun to test our larger scenes which take around 6 hours to bake.
update: Replaced the radiator block for an EK Velocity and added a little more paste (3 clicks) than before. Now the prologue is going a little better, with the PBO switch on in the cinema booster CPU to 4150mhz all core in the Cinebench R20 and to 4350 all core in CPU-z (both load CPU 100 percent as little fun it gets different clock, assuming cinebench uses heavier CPU instructions: D). In Cinebench, I peak at 75 degrees while a little lower in CPU-z. Get 9692 in cinebench when the computer is completely cold and 9615-9625 when the computer has been for a while, so it seems that the boost is temp sensitive even if you stay under throttle temps.