From all the arguments given, it seems that Mag's only chance at this is IF he can hold Thor in his armor. What if the armor that Thor wears is the sleeveless one he wore in The Avengers? What then? Thor's costume is mostly composed of boiled/stiff leather.
What happens if Thor just rips his shirt off when Mags starts controlling him? Remember that Thor is very strong, and although I do think Mag's can exert more magnetic force than Thor can via physical force, Mags is still going to have to fight for it.
Like I said before, I'm giving this to Thor on the simple fact that Thor has a chance of fighting back and surviving Mag's most powerful attacks... whereas Mag's has no way of surviving Thor's attacks. The whole strategy of Mag's would fall on whether or not he can manipulate whatever metal is in Thor's armor to stop and maybe crush him.