Phoronix posted a performance tests of FreeBSD 8.0 today. FreeBSD doesn't do very well there but the reason could be that it's first stable release of 8 branch and that it's currently stabilized and not that optimized for performance. Of course that is something else. As far as I know Linux distros use a lot newer and better GCC and FreeBSD uses a long outdated gcc 4.2.1 (20070719).