There are a couple of ways:

1) Don't use print in the first place

2) close STDOUT and open it again, sending it to /dev/null this time (assuming a unixy environment. (And print the benchmark to STDERR, if this isn't done already)

3) work around your problem by running perl script.pl|tail

Note that I/O is usually rather slow (compared to other operations), so changing I/O behaviour means changing your benchmark results.