Single CPU Results

Conclusion

The Pentium has about 64% of the core frequency compared to the Opteron (1.4 GHz to 2.2 GHz), which is slighty more than the ratio of the time for no threads (the points on the y-axis), considering the 6 seconds time for the Opteron as being the "true" one (this hasn't been the only CPU intense task on the Opteron). When using more than 10 threads, the time doesn't change significantly, but the ratio between the times of the Pentium and the Opteron goes down to 50%, which means that the Opteron can handle more threads better than the Pentium III.
Both CPUs had their worst result when using just one thread, with the curves slowly falling to the lowest value at about 10 to 12 threads for the Opteron and about 8 to 10 threads for the Pentium III.
So you're best off using more than 10 ("equal") threads on the Opteron and the Pentium III, at least if there is no big synchronizing overhead as it is case in this example.