An issue you havent discussed.
Several reccies have proved to me that the best route up Skiddaw is to go up either the gully to the north of millside and west of little man, (sheltered) which is faster than the main latrigg path, and a recent reccie said going up the path to carlside is faster still. Not surprising. It is the best part of a mile shorter. But if you try this, dont be tempted by the footpaths to millside, they are bad. Head far enough up the A591 to take the road to millside.
The heather off calva is a lot worse than it was 3/4years ago, particularly if you head straight for the sheepfold: but I am still convinced the best line across martcrag, and the caldew valley floor for that matter, is to skirt it on the west side then take a dead reckon beeline for the RH bank of the stream gully that points SE heading just east of blencathra summit. (dont have my bearings with me) I noticed in a reccie a couple of weeks ago, that for as long as you follow the spur line just west of south of calva more towards skiddaw house, the running is really fast and the heather is short, it is only when you turn for the sheepfold the problems start.
So I am guessing, but I think following that ridge almost to the bottom before turning for blencathra might give a good line of fast running to the bottom. It is certainly less steep than E of Calva, and the caldew is narrower.
Clough head: I have tried a couple of routes and never improved on going just left.
One more to consider is the route to red pike from yewbarrow
Conventional wisdom is to find a long traversing rake across patches of scree that hits the yew barrow/red pike col: Ive had a couple of goes at dropping straight down one of the steep grassy slopes between the screes from a couple of hundred feet height above the col, heading straight for red pike. It is shorter by a couple of hundred m but loses and extra 50 feet height. The descent is no worse than some of that scree crossing, and it can be wet after rain. Im guessing that it is quicker on a dry day.
Grey Knotts, just head straight north, it is fast all the way down! when low down stay on the ridge of one of the spurs, before dropping to the rough road to the quarry hitting it about 300m west of the quarry.