Try this. It should complete much more quickly unless all the required records are at the beginning of the file: 

#! perl -slw
use strict;
use Data::Dump qw[ pp ];
use Time::HiRes qw[ time ];
use File::ReadBackwards;

tie *FH, 'File::ReadBackwards', $ARGV[0] or die $!;

my $start = time;

my( $last, @a, @b );
while( <FH> ) {
    /\d+\t(\d+)/;
    if( $1 > 3 ) {
        unshift @b, $1;
        unshift @a, $last;
        last if @b == 7;
    }
    $last = $1;
}

print time() - $start;
print join ' ',times;

pp \@a, \@b;

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The start of some sanity?

In reply to Re: Faster push and shift by BrowserUk
in thread Faster push and shift by baxy77bax

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