Mine is also way slower than I expected, here just to be complete :)

cmpthese (-2, {
    sortfirst => sub {
        my @list = -5..5;
        @list =   sort { $a <=> $b } @list;
        @list = ((grep { $_ >=   0 } @list), (grep { $_ < 0 } @list));
        DO_CHECK and (Compare (\@list, [0..5, -5..-1]) or die "@list")
+;
        },
    grepfirst => sub {
        my @list = -5..5;
        my @pos = grep { $_ >= 0 } @list;
        my @neg = grep { $_ <  0 } @list;
        @list = ((sort { $a <=> $b } @pos), (sort { $a <=> $b } @neg))
+;
        DO_CHECK and (Compare (\@list, [0..5, -5..-1]) or die "@list")
+;
        },
    packunpck => sub {
        my @list = map { unpack "l>", $_ } sort map { pack "l>", $_ } 
+-5..5;
        DO_CHECK and (Compare (\@list, [0..5, -5..-1]) or die "@list")
+;
        },
    pryrt => sub {
        my @list = -5..5;
        sub sgn { $_[0] < 0 ? -1 : 1 }
        @list = sort { (sgn ($b) <=> sgn ($a)) || ($a <=> $b) } @list;
        DO_CHECK and (Compare (\@list, [0..5, -5..-1]) or die "@list")
+;
        },
    choroba => sub {
        my @list = -5..5;
        @list = sort {
            ((-1, 0, 1)[$a <=> 0] <=> (-1, 0, 1)[$b <=> 0]) || ($a <=>
+ $b)
            } @list;
        DO_CHECK and (Compare (\@list, [0..5, -5..-1]) or die "@list")
+;
        },
    });
[download]

              Rate     pryrt packunpck   choroba grepfirst sortfirst
pryrt     123672/s        --      -35%      -39%      -66%      -73%
packunpck 190037/s       54%        --       -7%      -48%      -59%
choroba   204244/s       65%        7%        --      -44%      -56%
grepfirst 367991/s      198%       94%       80%        --      -20%
sortfirst 460545/s      272%      142%      125%       25%        --
[download]