I'd be inclined to use join even if it were somewhat slower. However, my guess is that join is faster and actually, a benchmark bears that out:

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

my @strings = qw(
    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
    zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
    ppppppppppppppppppppppppppppppppppppppppppppppppppppppppp
    qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq
    rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
    sssssssssssssssssssssssssssssssssssssssssssssssssssssssss
    ttttttttttttttttttttttttttttttttttttttttttttttttttttttttt
    );

cmpthese
    (-1,
        {
        join => sub {join '', @strings},
        pack => sub {pack("a*" x ($#strings + 1), @strings)},
        }
    );
[download]

Prints:

          Rate pack join
pack  452302/s   -- -58%
join 1073851/s 137%   --
[download]