The cost depends a great deal on what you do with the argument list inside the sub/method. If you don't copy the argument list in some fashion then the hash construction can be expensive for more than a few parameters. However if you would otherwise copy the argument list into an array or hash inside the sub, the cost of constructing the hash is much less relevant. Consider:

use strict;
use warnings;
use Benchmark qw(cmpthese);

for my $argCount (2, 10, 100) {
    my @args = (1 .. $argCount);

    print "\nFor $argCount elements:\n";

    cmpthese (-1, {
            hashArg => sub {noCopy ({@args})},
            listArg => sub {noCopy (@args)},
            toList => sub {toList (@args)},
            toHash => sub {toHash (@args)},
        }
    );
}


sub noCopy {
}


sub toList {
    my @args = @_;
}


sub toHash {
    my %hash = @_;
}
[download]

Prints:

For 2 elements:
             Rate hashArg  toList  toHash listArg
hashArg 1066864/s      --    -12%    -27%    -74%
toList  1205941/s     13%      --    -17%    -71%
toHash  1459027/s     37%     21%      --    -64%
listArg 4106796/s    285%    241%    181%      --

For 10 elements:
             Rate  toList hashArg  toHash listArg
toList   344656/s      --    -14%    -17%    -91%
hashArg  399964/s     16%      --     -4%    -90%
toHash   416260/s     21%      4%      --    -89%
listArg 3846573/s   1016%    862%    824%      --

For 100 elements:
             Rate hashArg  toHash  toList listArg
hashArg   38850/s      --     -6%     -7%    -98%
toHash    41541/s      7%      --     -1%    -98%
toList    41895/s      8%      1%      --    -98%
listArg 1686904/s   4242%   3961%   3926%      --
[download]

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