Kala Patthar stands at just over 5500m, although not excessive time is invested at that altitude as being the trek then descends again right down to Pheriche and inevitably again to Lukla Airport.
Kathmandu is https://janebpoc433120.pointblog.net/the-smart-trick-of-everest-base-camp-trek-that-no-one-is-discussing-70261793