Simon,
Basically I use a measurement of approx a full hand span forward of the fwd beam.....that is about right for me anyway.
And I use Carbon extension....it takes a lot of punishment, even tolerate to being placed in a curve when swimming and usually returns to it's original shape.....unless ou are unlucky enugh to break it.
Material is personal prefernce....I absolutely loath the conduit ...
Enjoy.
David
"Banh Sidhe"