Most sites recommend a differential across the rad of 12C - but I wonder
if this was aimed at higher flow temperatures of yonder times?

I manage with flow of 55C most of the year - so what would be a sensible
differential to aim for? 8C?

I've also learnt that different lockshield valves vary massively - I
have one set that typically 1/2-3/4 turn is about right. Another set
tend to be happy at 1/4 and 3/4 is "practically fully open" as far as
temperature diffs go. Quite surprising...