I recently went through the same decision as well. I went with the 540's myself. The price difference was not that much. Purchased a new set off amazon and they did include a set of cleats.

The difference in weight was not really noticeable when holding a 540 in one hand and a 520 in another, was not too worried about weight. Did prefer the look of the 540 and the axle was a smaller diameter.

I do have to note, the 540 is much better than me last petal. I was using a dual platform/spd m324. Much smoother and no worrying about having to turn the pedal to click in.