I would expect CPU load to spike at 2 or less - just my experience with much less household activity.
Although this article doesn't address the issue directly, I am sorry I didn't think of this resource sooner:
http://wiki.untangle.com/index.php/NG_Firewall_Performance_Guide
Also, since I have never installed Spam Blocker, (Email settings apply only to the SMTP protocol) I didn't realize this:
from: http://wiki.untangle.com/index.php/S...hat_do_I_do.3FMy CPU load is always above 7. I still need to test for spam. What do I do?
Raising the number will allow you to test for spam, but will likely also increase the CPU load. If your CPU load is that high, that's an indication that your hardware may not be robust enough for your site. If your user count increased since you installed your server, or the volume of the internet traffic has increased substantially, this could be a cause. You may also have been spending as little for hardware as you could get away with. Regardless, you probably also are being impacted in other areas without realizing it. You should determine exactly what the hardware specs are on your server to determine whether you should supplement the existing hardware or replace it with something more robust.