If you try the same benchmark with the + modifier instead of the * modifier you will see which is truely fastest:

use Benchmark q{cmpthese};
my @arr = ( q{   fdsgehw fw wwfe w    } ) x 5000;
cmpthese -5, {
    "alternation*"   => sub {
        my @new = @arr;
        s{ ^\s* | \s*$ }{}gx for @new;
        },
    "alternation+"   => sub {
        my @new = @arr;
        s{ ^\s+ | \s+$ }{}gx for @new;
        },
    capture       => sub {
        my @new = @arr;
        s{ ^\s* (.*?) \s*$ }{$1}x for @new;
        },
    splitJoin     => sub {
        my @new = @arr;
        $_ = join q{ }, split for @new;
        },
    "twoStage*"      => sub {
        my @new = @arr;
        s{ ^\s* }{}x for @new;
        s{ \s*$ }{}x for @new;
        },
    "twoStage+"      => sub {
        my @new = @arr;
        s{ ^\s+ }{}x for @new;
        s{ \s+$ }{}x for @new;
        },
    "twoStageComma*" => sub {
        my @new = @arr;
        s{ ^\s* }{}x, s{ \s*$ }{}x for @new;
        },
    "twoStageComma+" => sub {
        my @new = @arr;
        s{ ^\s+ }{}x, s{ \s+$ }{}x for @new;
        },
    };
[download]

                 Rate alternation* capture alternation+ twoStage* twoS
+tageComma* splitJoin twoStage+ twoStageComma+
alternation*   29.8/s           --     -1%         -18%      -34%     
+      -35%      -44%      -65%           -66%
capture        30.2/s           1%      --         -17%      -33%     
+      -34%      -43%      -64%           -66%
alternation+   36.4/s          22%     20%           --      -20%     
+      -21%      -31%      -57%           -59%
twoStage*      45.3/s          52%     50%          24%        --     
+       -1%      -15%      -46%           -48%
twoStageComma* 45.9/s          54%     52%          26%        1%     
+        --      -13%      -46%           -48%
splitJoin      53.1/s          78%     76%          46%       17%     
+       16%        --      -37%           -40%
twoStage+      84.6/s         184%    180%         132%       87%     
+       84%       59%        --            -4%
twoStageComma+ 87.8/s         194%    191%         141%       94%     
+       91%       65%        4%             --
[download]