just hypothetically...I've only given it about 2 minutes of thought...
6 classes based of of the Modern class system...feats for magical abilities...
2 levels of feats for magic, one gives you a slower progression (ie. ranger, paladin) and a second gets you full magic user progression...
3 sets of feats, 2 varieties of each...for example:
1st feat charisma based arcane - slow progression
2nd feat charisma based arcane - fast progression
spell tables would have to be thought out for each progression.
just my random thoughts worth...
DanZilla