[thegrim33]

Except everything in orbit is also moving at those same speeds, so the relative speed difference between any two objects is orders of magnitude smaller than that. (Of course, yes, there's outlier cases where that's not as true, but those are the rare exceptions to the rule; the constellations being discussed don't fall into the outlier cases).

[notahacker]

Well yeah, the relative velocity is what matters, but not everything is moving in perfectly circular concentric shells either. You've got many different inclinations and eccentricities (and drag profiles) within what's broadly construed as "LEO". The relative velocity of the Iridium 33 / Kosmos 2251 collision involving two satellites in LEO was over 11km/s.