To reinforce Joules' post, if, as I pointed out, you output the image from the low density sensor to the same size as that from a high density sensor, the fast moving subject will have moved an identical amount across the same-sized photos from both and have the same motion blur.
You also missed out the key part of my sentence and quoted only the irrelevant part to this discussion: "If the conditions are right - good lighting, high shutter speed for a moving subject or good tripod for a static at low speeds, and a good wide lens, the higher resolution sensor will give better images that can be used at larger output size or greater cropping. Whether it will be of any advantage to you personally, that is another matter. "