With HMMer, one of the scientific benchmarks in the Phoronix Test Suite, OpenIndiana scaled better at six cores with Hyper Threading compared to the three other operating systems. There was not much deviation in the scaling performance -- except for PC-BSD again at three and four cores -- until the operating systems hit six cores.
The Fortran-written NAS Parallel Benchmarks and its FT.B test had scaled much better on Fedora 14 as the core count increased compared to the other operating systems. CentOS 5.5, PC-BSD 8.1, and OpenIndiana b148 scaled at close to the same rates, sans PC-BSD at three and four cores. Worth noting though is that all four operating systems were negatively affected by Hyper Threading on the Intel Core i7 CPU with this test.
The LU.A result for the NAS Parallel Benchmarks is particularly interesting. PC-BSD 8.1 outright fails (and is certainly reproducible with the Phoronix Test Suite) at three and four cores, but it pops to perform very well at six cores. With six cores plus Hyper Threading, its performance sharply falls again as does the OpenIndiana operating system. The two Linux operating systems were relatively uninteresting with this particular sub-test.