18m has far less power than the 16m, at least on the V8. Only version I played with back to back.
Not crazy about above poster recommending a 4 pound difference in a hybrid of Gut and Poly. They’re already going to drop tension at hugely different rates. One week of play and it’s going to easily be a 20 point tension difference with the different material properties.
A pro who plays new strings all the time and isn’t buying his racquets, nor storing them strung for potentially weeks at a time is a very different story.