If you're got a 5th account, and if those 4 mixed characters are on separate accounts - I'd almost go and power boost them through SM to quick get them to 40. If you start with Library (the lower level toons should get xp faster than the highest). Once the xp rate sucks, move on to Armory/Cathedral. They should level out and stop getting xp just past 40 (I'd keep all 4 with me to level out the GroupLevel/XP curve).