Those were probably four engine Boing 707s and Douglas DC-8s with water alcohol injection during take offs. Their climb was calculated with a single engine out. Today that would be 50% of your max. power instead of 75% of theirs. Still I don't think I'd like to try it. I remember my first time between Christchurch NZ and Sidney, Australia via Canberra. We off-loaded in the middle of the night in Canberra and had enough fuel to make it to Sidney so we cranked up with out going into flight operations and departed. We didn't have good charts of the area so we were oblivious of a hill aligned with the runway. I was pitch black out. We climbed straight out and cleared it without knowing what we did. After a few day we had to go back to Canberra, pick our cargo of two helicopters and fly to Darwin. We were now heavy with fuel and the "whomp-whomps". When we lined-up on the runway we saw "Mt. Everest" out there and asked the tower how far it was and how high. We took off and could tell that at that with the extra weigh we were not going to clear it so we had to jog around it. Made it no sweat but I learned a good lesson that day that I never forgot