This is how I have been doing my PowerPro Spectra, very simple using Sullivan 80# clips. Never had a line failure or knot come loose. And no fraying.
I have been using 65# test Spectra lines, even on my heavy Vector 40 at 62 oz. Concerning overall strength, two 65# test lines to a model would total 130#. In level flight, my Vector probably has a pull of say 10# (5# per line). Or a safety factor of 13.
Some pilots are using 80# test. The only reason to do so that I can think of would be for lower stretch. But 80# is surely not needed for overall strength.
Also, lines can end up with slight damage over time (dragging lines on the ground, someone maybe stepping on them, etc.). I can make up a new set of lines for around $5. So, I have been replacing my lines that have lots of flights on them every couple of years. Just additional safety factor overkill for me.