Not as exciting an improvement as I'd hoped:
4 GB RAM Intel(R) Core(TM)2 Quad CPU Q9300 @ 2.50GHz make -j5 real 7m35.985s user 24m54.741s sys 3m15.628s
6 GB RAM model name : Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz make -j9 real 4m39.577s user 30m43.651s sys 2m30.109s