I have an olympus OM-D E M10 Mirrorless digital camera with 14-42mm 2RK lens, and I have a 1/250 shutter speed limit. Now my question is, what kind of moving models can I freeze with that shutter speed?
In terms of freezing movement in a photo, the only measurement that counts is angular distance. That is, it only matters how much the angle of the subject changes with respect to the optical axis of the lens in the time the light from the subject is allowed to fall in the recording medium (usually a digital sensor or film). If the subject moves less than the width of the smallest unit on the recording medium, such as a single pixel on a digital sensor, it will appear to be motionless.
This can be visualized by taking a moderately long exposure while riding at high speed in a car. Be sure someone else is driving the vehicle. Set a shutter time of about 1/60 second, point the camera sideways out a window, and take a photo with an aperture and ISO appropriate for proper exposure. The shoulder of the road and other items very near the car will be blurry. The clouds or mountains in the distance will appear motionless. How can this be? In linear terms your speed relative to the shoulder of the road and those far off objects is the same (assume for a moment there is no wind moving the clouds at any significant speed). But in angular terms the nearer an object is to the camera the further it moves in relationship to the camera's optical axis. The very near objects that were on the far right at the beginning of your 1/60 second exposure time are on the far left by the end of that 1/60 second. But the very far objects have likely moved less of an angle than the amount you've allowed the camera to move while holding it for 1/60 second.
At 1/250 second objects that are close will begin to show blur at much slower speeds than objects that are further away. If you must fill the frame with your subject using a 14-42mm lens, then larger object can be shot from a greater shooting distance and will be able to move faster than smaller, nearer objects before beginning to show blur.