I imagine it also depends on weight. At most, Peridot has been shown moving probably what, 2 tons of 's highest shown lifting ability has been around ten tons with adequate focus using her ferrokinetic powers. According to the wiki it's standard magic and not magnetism itself since her tablet didn't get fried by the magnetic field needed to levitate it, but the tablet's components might also just be shielded.
I think she'd probably be the surprise holdout in a 1v1 fight with Iron simply because she might not be able to damage him but could avoid getting hit a lot longer using her ability to make him whiff his attacks until he adapted.
She'd probably be the gremlin queen of the area cobalts though.