Is on a deceptive slope but it feels and looks flat, so not surprising you felt sluggish on the way out and speedy on the way back!
Must be nice to hit that path at the end of the Lairig Ghru, would have loved to see how quick you were running down there in last year's race!
Much slower than you will be when you get around to racing it! I think I ran the last 10k in about 35 minutes. It is a nice bit of running after the rocky path through the LG.