Thanks for fixing the RC; it's slower; + RAM now at ~13.5 Mb vs. mine of ~10 Mb according to my crude measurements.

use strict;
use warnings;
use Benchmark 'cmpthese';

cmpthese -3, {
    am => sub {
        my ( @a, %h );
        open my $fh, '<:raw', 'unixdict.txt' or die;
        while ( <$fh> ) {
            next unless length > 6;
            chomp;
            ( -1 != index $_, 'e' ) ? ( push @a, $_ )  :
            ( -1 != index $_, 'i' ) ? ( $h{ $_ } = 1 ) : 1
        }
        close $fh;

        my ( @ret, $i );
        exists $h{ $i = tr/e/i/r } 
            and push @ret, sprintf "%30s  %s\n", $_, $i 
                for @a;
        @ret
    },
    rc => sub {
        my $file = do { local (@ARGV, $/) = 'unixdict.txt'; <> };
        my %i = map { tr/e/i/r => sprintf "%30s  %s\n", $_, tr/e/i/r }
          $file =~ /^(?=.{6}).*e.*$/gm;
        @i{ split ' ', $file };
    }
}

__END__

     Rate   rc   am
rc 25.2/s   -- -65%
am 71.1/s 182%   --
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