URL reputation is a separate subsystem from antispam. The scores are not cumulative between the two. If you have spam that isn't getting picked up, the first thing I would recommend is try lowering your threshold for action from 5.0 to 4.2 and seeing if that makes a difference. You can also submit spam samples to the McAfee Labs team for analysis and inclusion in future rules updates. See http://kc.mcafee.com/agent/index?page=content&id=KB59415 for more information on how to do so.