Simtech wrote on Sep 15^th, 2018 at 5:58pm:

I just thought that by using more flaps the rotation speed is lower for shorter rwys.

I think the 707 is generally not suitable for "short" runways. You will not really gain RWY-Meters with high flaps settings. I never choose a runway shorter than 8.000 feets - and this is really barely for the 707  ;)

I think it is possible with very few fuel and no payload to take off from a 6000 field, but never tested.