I was configuring Apache spam assassin and ran some tests on what setting works best for me.
1.6 is the magic number.
Some say may think this may be too aggressive of a setting. Try it. You will find that legit emails get through and the majority of spam won't get through. The only junk mail that gets through will be the ones where the entire email message is an image that is sent from a domain not on the black lists yet.
1.5 setting is too aggressive though, and a legit email from gmail won't even make it through the filter.