Talking of strength, I have been using 2 mm diameter for over a decade. I originally supplied rudders with 3 mm (~1/8") but that is over-kill.
7/64" works out for me at 2.7 mm.
The first Mac50, built over a decade ago by my partner, still has the original rudder lines as does my other kayak which is a year younger. What hasn't been mentioned is where others have had breaks or wear with Spectra lines.