Nord3d
CPU: i5 2500K @4.7GHz
RAM: 8Gb DDR3-1600 Dual-channel
Ubuntu 10.10 x64
Houdini 11.1.147 Linux x86_64 gcc4.4

Render Time: 22:59.70u 8.26s 5:49.56r
Memory: 42.53 MB of 43.21 MB arena size. VM Size: 262.68 MB

Same machine, Ubuntu 12.04 x64, Houdini 12.0.661

Render Time: 7:56.44u 0.50s 2:02.15r
Memory: 136.05 MB

It looks like H12's stochastic transparency setting being on by default speeds up this render quite a bit, but gives lower quality results.

Default benchmark.ifd (shaders compiled for H12)
Render Time: 20:19.82u 0.92s 52.74r
Memory: 688.28 MB

With stochastic transparency OFF, the resulting image looks closer to Peter's original, but still not quite the same. (shadows aren't as defined)

Render Time: 32:35.59u 0.72s 1:23.44r
Memory: 688.28 MB

This is on an EVGA SR-2 with dual E5645's @ 3.6Ghz.