Andy,
I would suggest trying the LogSpiral script.
Set the exponent to something like .08, adjust to suit.
Set the number of Whorls to say 3.26.

Then place a vertical circle on the open end, say 2 units. Adjust radius to suit.
Sweep the circle along the spiral, using Pointed End checkbox.

Slice off the amount of 3D curvature desired.
Instead of a circle, a partial curve could be used instead...

Due to MoI's built in history, after the sweep, the radius of the circle can be changed, and the sweep also changes.

- B