For a good player everything under 320 is too low. With a stiffer punchy racquet you can get away with 315sw as a total minimum, just to hold the ball coaching and similar, but you have to swing out of your heels all the time. Only from 325sw can you play more normally if you like to drive through and attack, and that's also with a stiffer punchier racquet, such as Aero VS or Ezone 98. For players who like to hold, block, slowball and counterpunch with a doublehander a 320sw stiffer Radical can work well if they're quick, but not lower, but they risk having their serves attacked all the time
So basically 325 is a starting point, and can work for stiffer punchier racquets, but flexy racquets - and 18x20s - will still feel weak below 330, for a Blade v8 98 18x20 starting point is more like 335sw, same with Speed Pro, but both feel nice only at 340, esp Speed Pro. A flexy Prestige 98 18x20 320g is also half dead at 335sw, 340 is a starting point kind of
Haha I also remember trying to play with a Microgel MP a tennis friend played with since juniors, and I played with RF97s and 340g Pro Staffs for a long time, felt like a total fly swatter, and I really couldn't understand how can he even play with it, and his balls were really weak for me. And also I honestly thought for many years that I don't somehow understand something crucial, seeing those light racquets everywhere around me, didn't know much about specs either when I was younger