I think for the adren and athro the leveling should be modified so it is more challenging, I mean if you guys are still using FF as a platform to get people good enough to be in BD then it is a proving grounds, and if any of the people are in BD already then I definatly recommend it be increased because of the ease of leveling now, compared to back in the day.
for levels 1-40 they should level to 50, from 40-55 they should gain 10 levels, 55 and beyond they should gain 5 levels. it is extremely fair considering the ease of leveling. If you wanted to make it very difficult, add a time limit, a level a day is fairly easy up to lvl 80 without a gau provided you have the resources to pay for ammo.