cmpthese( -1, {
    k1 => sub { $foo->do_nothing(1) },
    k2 => sub { Foo->do_nothing(1)  },
    k3 => sub { Foo::do_nothing(1)  }, 
    k4 => sub { do_nothing(1)       },      
    k5 => sub { &do_nothing(1)      },      
});

##</code><code>##

        Rate   k2   k1   k5   k3   k4
k2 1380806/s   -- -14% -34% -35% -37%
k1 1610612/s  17%   -- -23% -25% -26%
k5 2103412/s  52%  31%   --  -1%  -4%
k3 2133262/s  54%  32%   1%   --  -2%
k4 2181254/s  58%  35%   4%   2%   --