If you check my postings on this, you'll see that I wrote: They have less back bow.
Well, the Staystrate lines have only 3 strands. This means that even though measured diameter is same as with 7- or 19-strand lines, the average frontal area is less. That makes air drag smaller.
But, they have less metal per cross area. Anyway, the elognation under tension is less than with stainless steel lines because of stronger piano wire material.
Another but, they are clearly heavier than stainless .015's, the weight comes from the tin solder. That also contributes to the flexy feeling.
I used Staystrates for a while but stopped because they needed too much attention, especially when flying alone.
In the beginning I used to polish the new lines with ScotchBrite or similar, that made them a lot smoother, but because it partially broke the tin coating, the steel started to corrode and they were not so smooth anymore.
The manufacturer recommended to wipe the lines first with an oily rag (WD40) and then polish with dry cloth. That'sperhaps OK for combat & team racing.
Some of the russian carbon steel lines are very good, but beware, there are several types. The best has 4-strands and rather coarse coil.
Just random thoughts.. L