When he is 4~10 lvls higher, every successful attack gives 5 exp
when fighting 100 atk/def vs 100 atk/def, the chances of winning are 41.67% (the rest is tie or lose)
thus I get on average 2.08 exp per attack, slightly higher than the average exp from explore and much faster (just click 'attack again' ;P)
I wanted to reclaim my throne