John,
I don't know if you and cazatou are being deliberately evasive. The only reference I have made to speed is that given by Bill Wratten, as "too fast for the conditions". Unless we know exactly what the conditions were at waypoint change how can we determine what is "too fast"? If we could agree that, we would then need to know that they were going that fast.
For all I know, or anybody else as far as I can see, they may have been able to see clearly up the coast towards Gigha at that point.
Of course, it may be that you are saying that flying at an IAS of 135 kts within 1.75km of local cloud, regardless of what else you can see, is grossly negligent, even if they were intending to make a small heading change based on the new waypoint. I would disagree with you but my opinion on that would be of little value to this discussion.
p1