I'd leave the out thrust, it is really the end of the world when the lines go slack. Using one less cell in the battery usually makes the flight a little longer. Less load, or a smaller diameter/pitch prop helps. Smaller motor... Most of these things will make the plane lighter too, so it will fly better and not hit the ground so hard if things happen. Oh yes, longer lines are all right too. Just remember you want a good pull, and not having the lines go slack.