[ThinkingPlus]

I don't think that swing speed is the deciding factor to sustain the pre-stressed clubshaft bend after Start Down. Sustain the Lag and you sustain the bend. Look at Lee Trevino in "Pros at Impact". That amount of Bend is not caused by speed.

I do think that regular or more flexible shafts can show more flex at impact but thats because they aren't stiff enough to rebound after the initial Start Down Bend.

Sustaining lag and hence bend is not a function of swing speed, but of technique (agree), however, magnitude of bend is a function of acceleration as well as shaft flex. Greater acceleration produces greater swing speed unless a countering deceleration occurs prior to impact (loss of lag).