poly and spin
Re the earlier posts re rec players not being able to tell the difference or make the most of increased spin from changing strings, that's bunk.
I play 3.5/4.0 singles. I'm old (47) and no monster (155#) but I have good racquet head acceleration and my baseline game is based on heavy, defensive spin.
I play with a POG OS, very open pattern.
I have strung this racquet with full gut, full multi, full poly and just about every hybrid choice imaginable, at every tension imaginable. After 6 months of syngut mains and poly crosses at around 50#, I was missing spin and went back to full poly at 45#.
I have significantly more spin with this setup. I see it and my regular opponents comment on it without me mentioning the change.