According to the release notes, the McAfee Agent 4.6 release was developed for use with:
McAfee ePolicy Orchestrator 4.5 and 4.6
Agent 4.6 will give more functionality when you do eventually upgrade to 4.6 epo. You might as well deploy 4.6 agent if your going to be upgrading agents.
btw, I'm running over 70k nodes with Agent 4.6p2 and ePO 4.5.5 with no issues.