But now you're not playing fair :)

The diff is very much depending on what the first arg is, and how common is a first argument of a string of 1 Mb?

 $a1 = "a" x 1e6";

         Rate    var    und    skp
var   11049/s     --  -100%  -100%
und 2812991/s 25360%     --   -20%
skp 3495253/s 31535%    24%     --

 $a1 = "a" x 1e4;

         Rate  var  und  skp
var  701455/s   -- -75% -80%
und 2840570/s 305%   -- -17%
skp 3440640/s 391%  21%   --

 $a1 = "a" x 100;

         Rate  var  und  skp
var 2055647/s   -- -28% -43%
und 2858267/s  39%   -- -21%
skp 3633679/s  77%  27%   --

 $a1 = "a";

         Rate  var  und  skp
var 2075800/s   -- -25% -41%
und 2780315/s  34%   -- -21%
skp 3528861/s  70%  27%   --

 $a1 = 1;

         Rate  var  und  skp
var 2293760/s   -- -14% -31%
und 2672341/s  17%   -- -20%
skp 3340426/s  46%  25%   --

 $a1 = undef;

         Rate  var  und  skp
var 2429401/s   -- -14% -30%
und 2840570/s  17%   -- -18%
skp 3479788/s  43%  23%   --

 $a1 = sub { 1; };

         Rate  var  und  skp
var 2383127/s   -- -16% -32%
und 2824827/s  19%   -- -19%
skp 3508785/s  47%  24%   --

 $a1 = bless { a1 => 1 };

         Rate  var  und  skp
var 2383127/s   -- -18% -31%
und 2912710/s  22%   -- -15%
skp 3429921/s  44%  18%   --
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