Nehalem machines are very fast
I've just had a chance to use a Nehalem HP Z600 workstation with 2 Xeon E5520 CPUs. The machine has 8 cores, 16 hardware threads, and an absurd 12 GB of RAM.
It's very fast. It's about 2.5 times as fast (when building the Android sources) as the previously fastest machine I'd used, which was an HP xw6600 with a single Xeon E5420 CPU.
The machine's relatively small, no larger than an ordinary ATX tower. One way that HP kept the case small is by making the motherboard an odd shape: it is "C" shaped, with a cutout that leaves room for the DVD drive.