You can probably speed up the "_r" versions a little by removing unnecessary "+"s. For example, change

            $str =~ s/\s+/ /g;
            $str =~ s/^\s+//;
            $str =~ s/\s+$//;
[download]

to

            $str =~ s/\s+/ /g;
            $str =~ s/^\s//;
            $str =~ s/\s$//;
[download]

Update: The improvement is quite substantial. Without the +, it ties 3-sp for fastest for short strings, and it's 42% faster than second fastest for long strings.

Short string:
            Rate   3-sp_r 3-sp_r2  3-sp
3-sp_r  329182/s       --    -14%  -14%
3-sp_r2 382305/s      16%      --   -1%
3-sp    384541/s      17%      1%    --

Long string:
           Rate   3-sp 3-sp_r 3-sp_r2
3-sp    20911/s     --   -12%    -38%
3-sp_r  23687/s    13%     --    -29%
3-sp_r2 33582/s    61%    42%      --
[download]