The hardest levels to grind are 50 to 60 and then 60 to 70. If you grind writs like a robot and just fight and kill with little down time the 50s can be done is 60 hours of game play and the 60s can be done in 100 hours of game play. The level cap is about to go to 80 I would expect the grind to 80 would be much more lengthy. The grind of the first 50 levels is trivial at best these days.
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