This "way to do it" uses a hash to find the highest number:

use strict;
use warnings;

my %candidates;
while (<DATA>) {
    push @{$candidates{$1}}, $_ if /^\s+(\d+)/;
}
my ($highest) = sort {$b<=>$a} keys %candidates;
print for @{ $candidates{$highest} };

__DATA__
High fanout nets in the post compile netlist:
    Fanout  Type          Name
    --------------------------
    2       INT_NET       Net   : c_c
                          Driver: c_pad
    2       INT_NET       Net   : b_c
                          Driver: b_pad
    2       INT_NET       Net   : a_c
                          Driver: a_pad
    1       INT_NET       Net   : sum_c
                          Driver: sum_1_SUM0_0
    1       INT_NET       Net   : N_5
                          Driver: sum_1_CO0_i
[download]

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)