Benchmark in what way? GUI/Modelling/Display Performance or Rendering [Mantra?] Performance? I'll ask sidefx to see if they have some sort of internal benchmark script or something.
At Work I use a R12000 300mhz Octane 512MB ESI box and a P3 450mhz 384MB Oxygen VX1 box at home. I'm setting up H4 tonight at home for some tests and I'll compare the two platforms to my experience.
I guess a benchmark could be the raytraced houdini logo scene that fires up when you open a new houdini 4 session.