Thanks everyone. I tried the fence line/sheepfold route last week and was amazed by how good the trod was. How did I miss it before?!!

Comparing it to my S/SE route through the heather, the fence line route is about 45 seconds quicker and far more runnable, but quite a bit longer and you lose an extra 25m of height. It is also more reliable, as the heather is so deep going S/SE that you have absolutely no idea where your feet are going.