use Benchmark qw(cmpthese);

cmpthese(-2, {
        fs => sub { delete $INC{'File/Slurp.pm'}; require File::Slurp; File::Slurp->import(); $x = read_file("foo") },
        is => sub { $x = do { local (@ARGV, $/) = "foo"; <> }; }
});

---

$ perl5.6.0 test.pl
Benchmark: running fs, is, each for at least 2 CPU seconds...
        fs:  3 wallclock secs ( 2.08 usr +  0.11 sys =  2.19 CPU) @ 266.67/s (n=584)
        is:  2 wallclock secs ( 1.16 usr +  0.86 sys =  2.02 CPU) @ 47311.39/s (n=95569)
      Rate     fs     is
fs   267/s     --   -99%
is 47311/s 17642%