Amit Bhai Khardung La is only a matter of 10 mins staying at the top and climbing 35 kilometers from Leh. Nubra Valley is at an even lower altitude than Leh city that is why reaching there first is recommended. Pangong is also a place where most of the people suffer from AMS because it is at a very high altitude . So stick to your original plan of going to Nubra first and then to Pangong. Do not do it the other way around.