I do not suggest that you use any results shown here to make decisions about your own production system(s).
There are a number of things about these tests that mean that they’re not directly applicable to the real-world.
1. Everything’s running off one disk, and hence one disk controller.
2. I haven’t gone out of my way to tune the Solaris install.
3. The SMTP traffic is being generated by the same machine that’s receiving it.
4. The test machine is running a number of services that you wouldn’t expect to see on a real mail server. For instance, a GNOME desktop, web browser, and so on.
However, you should be able to use the methods shown here to generate data about your production systems, and make a decision accordingly.