($chunk) = substr($string,0,201) =~ /(.*)\s+\w*$/',

##</code><code>##

Benchmark: running Hofmator, MZSanford, japhy, tye, each for at least 3 CPU seconds...
  Hofmator:  3 wallclock secs ( 2.99 usr +  0.01 sys =  3.00 CPU) @ 206100.67/s (n=618302)
 MZSanford:  4 wallclock secs ( 3.03 usr +  0.00 sys =  3.03 CPU) @ 55936.63/s (n=169488)
     japhy:  4 wallclock secs ( 3.00 usr +  0.00 sys =  3.00 CPU) @ 256036.67/s (n=768110)
       tye:  4 wallclock secs ( 3.00 usr +  0.00 sys =  3.00 CPU) @ 292146.67/s (n=876440)

##</code><code>##

#!/usr/bin/perl
use Benchmark qw/timethese/;
 
$string = q/Some text repeated / x 50;

timethese(-3, {
    MZSanford => '$chunk = substr($string,0,201);$chunk =~ s/\s+\w*$//',
    Hofmator  => '($chunk) = substr($string,0,201) =~ /(.*)\s+\w*$/',
    japhy     => '($chunk) = $string =~ /^(.{1,200})(?<!\s)(?!\w)/;',
    tye       => '($chunk) = $string =~ /^(.{0,199}\S)\s/',
});