http://www.serebii.net/pokedex-dp/308.shtml
According to serebii, Medicham has 240 max base attack. With pure power, that is 480. Where did this 720 max attack come from? Even adding 63/126 extra onto those numbers assuming Serebii didn't account for EVs (it looks like they did btw) someone is wayyy overestimating Medicham's base attack.
Anyway, lets use this as a resource:
Stat = floor((floor((Base * 2 + IV + floor(EV / 4)) * Level / 100) + Num) * Nature)
Assuming 252 or 255 EVs and 31 IVs (best case for Medicham) and we got:
Medicham: floor((((120+ 31 + 63) * 100/100) + 5) * 1.1) == floor(240.9) == 240 x2 from Pure Power == 480 base attack.
Hitmonchan: floor((((210 + 31 + 63) * 100/100) + 5) * 1.1) == floor(339.9) == 339 base attack. x 1.3 from Iron Fist (more or less) == 440 base attack
BTW: This makes Gallade only about 100 base attack less than Medicham. Not 200 less :-/
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So what does Hitmonchan get that Medicham doesn't?
Close Combat. Ironically not a punching move :-/ Too bad Medicham's high jump kick does more.