I had 3 times a boom strike on my Raptor 90's. I tried to make them stiffer and stiffer during this process :-)
Now I am running a metal hub with the Carbon Extreme dampers. This seems to be fine with 9 degrees cyclic on the roll axis, and 8 degrees on the elevator axis.
Note that I am running very light paddles, and I was running 10 degrees on the cyclic. You can find pictures of the mess at: http://www.rchelicopterweb.com/Crashes/CrashResults.htm
The main problem is the plastic main hub which wobbles on the main shaft, and of course the soft dampers.
P.S. the Hirobo had major problems with this also, they even made the new main shaft which was longer to keep the blades further from the boom.