May I suggest running this in a Virtual Machine such as VirtualBox. Then you can control how many cores are pegged by how many you have assigned to the VM, and leave the rest of your machine responsive for other things.
2011-11-16 23:41:13 UTC (ports tree)
2011-11-17 01:10:16 UTC (RELENG_7, 7.4-STABLE)
2011-11-17 00:36:10 UTC (RELENG_8, 8.2-STABLE)
2011-12-01 21:13:41 UTC (RELENG_9, 9.0-STABLE)
2011-12-01 21:17:59 UTC (RELENG_9_0, 9.0-RC3)
2011-12-23 15:00:37 UTC (RELENG_7_4, 7.4-RELEASE-p5)
2011-12-23 15:00:37 UTC (RELENG_7_3, 7.3-RELEASE-p9)
2011-12-23 15:00:37 UTC (RELENG_8_2, 8.2-RELEASE-p5)
2011-12-23 15:00:37 UTC (RELENG_8_1, 8.1-RELEASE-p7)