The Droga guide reminded me to add this link:
Nurgalopedia (http://pub116.ezboard.com/fcouncilofzarchonfrm4.showMessage?topicID=4.topic)
Tier 5 is good exp at 65; Tier 4 for 60-62. I am not sure about the lower tiers, but tier 1 is mostly light blue at 52, so I am guessing would be worth a shot at 49.