Katsudon im actually reallly good at 5v5 and 3v3 but in my opinion 3v3 is alot harder, You get ganked more, Not as many team mates to help you, Get chased alot easier as the map is smaller and some other stuff :P
I cant play 5v5 on my iLoL mac client it fucks up at the end and goes 1fps and i cant do anything ;(