F5 gets you airborne quicker, but with a worse climb angle. If you look at the Take-Off Performance tables for runways, very often the runway is Obstacle Clearance limited, and it is this that limits take-off weight. So the F5 take-off is more limited. With F1, the take-off run is slightly longer, but once airborne, the climb is steeper, so the take-off weight is usually much higher. It can make quite a difference. The improved climb table gives you higher weight, and I think more reduced power take-off saving engine wear.