you should leave your shutter on 1/60th
1/60th if he's shooting 30fps, but 1/50 for 24fps.
As i see it the problem of the original poster was about the strobing effect due to higher shutter settings.
This has al to do with the freq. of the powergrid and nothing to do with the prefered shuttersetting for motionblur.
All light sourches directly connected to the powergrid will resonate at 60hz(50hz in europe) that is why if i'm shooting in the usa i would have to use 1/60th even when i'm shooting 25p.
Maybe that is the reason some people experience light flicker in the US when shooting 24p at 1/50th