As poj suggested, in these modern days importing into a relational database like Microsoft Access or sqlite might provide an easy SQL solution to your problem. If you want to look at your files as a text database then the problem looks like it fits an old text database processing tool: Awk. Perl has an awkish/autosplit '-a' mode suggesting:

#!/usr/bin/perl -a

use strict;
use warnings;

our %recs;
my $k = join "\t", @F[0 .. 3];
if ($recs{$k}) {
    $recs{$k}->{key_count}++;
    $recs{$k}->{rec}->[$_] += $F[$_] for 4, 5;
}
else {
    # careful to copy with [ @F ] not \@F here
    $recs{$k} = {key_count => 1, rec => [ @F ]};
}

END {
    $recs{$_}->{rec}->[4] /= $recs{$_}->{key_count} foreach keys %recs
+;
    print join("\t",@{$recs{$_}->{rec}}), $/ foreach sort {
        $recs{$a}->{rec}->[ 0 ] cmp $recs{$b}->{rec}->[ 0 ] ||
        $recs{$a}->{rec}->[ 1 ] <=> $recs{$b}->{rec}->[ 1 ] ||
        $recs{$a}->{rec}->[ 2 ] cmp $recs{$b}->{rec}->[ 2 ] ||
        $recs{$a}->{rec}->[ 3 ] cmp $recs{$b}->{rec}->[ 3 ]
    } keys %recs;
}
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