Ok everyone - we've all got ipads and phones at least with flight planning software etc. If you climb to your cruise altitude and are on a 400nm leg - your GPS tells you that your descent to destination is 50fpm and that number goes up as you get closer to your destination. So if you waited until you had 100fpm descent to destination - and you then set up a 100fpm rate of descent, you'd pick up at 5 knots most likely - at the same fuel flow - or you could go the same speed and throttle back - I did that once and could maintain the same groundspeed and burn 0,7gph less. obviously with terrain and airspace obstacles maybe its the not the most practical . . . but it does provide an interesting flight planning choice. Climb to 8500, start a 100fpm descent to 500 - its 80min - maybe its a way to stretch a fuel supply!