With everything else, you have to take this with a grain of salt, but I did what my favorite past time is when I want to see if one thing is faster than another and I Benchmark'd it. The difference is in the buffering since there is output being sent to a filehandle. I ran this about 10 times and these are the average results. (Most of the output has been removed for brevity). So using the following code, I got the following results:

use Benchmark qw(cmpthese);
my $tests = -25;
sub single { print 'This is a test'; }
sub double { print "This is a test"; }
cmpthese($tests,{
 single => \&single,
 double => \&double
 });
__OUTPUT__
            Rate single double
single 1952135/s     --   -16%
double 2313034/s    18%     --
[download]

As has been pointed out in other posts, the difference is nominal.