I'm new to SA, and currently testing it in order to integrate it with our systems.
The performance appears to be very bad - 6 messages per second.
I'm running SA 3.0.1 on DL380 - dual CPU, hyper thread, 4G RAM, with Redhat 8.
spamd is running with the rules engine only, and with most of the rules from SARE, beside bigevil.
The CPU is in 0% idle most of the time, and I have 3 spamc proccesses on the same machine. (when I run this with Java application instead of spamc I receive the same results).
1) You said you have 3 spamcs, but How many spamd's do you have, and how large is their memory footprint?
2) you claim "rules engine only". What exact settings have you changed to ensure this?
3) As a test, you might want to back out all of SARE's rules and check your message processing speed with stock-rules only. That should be very fast.
If it is fast without SARE, then one of the SARE rulesets is bogging you down, try adding them back one at a time.
If it is not fast without SARE, you have other problems, and you probably have some high overhead subsystem running. (the answer to 2 may prove useful here.)