When should I start training at Oblivion 4?

Not really, the map sucks, the exp:hp ratio sucks, and they do more dmg, and have 3 different attacks.
I see no reason for it to be better unless you are an F/P Mage...
Edit: AND they are weak to fire, neutral to everything but poiso...zzzz.... I say they suck

Their attacks are practically full-map, the mobs are lesser, not as many safe spots, man this is boring. O2 sucks except for time pieces, and you'd probably get those faster at chiefs of memory/regret.