Therefore, it is entirely to be expected that just one process, on my end, will be able to handle the 2,000 separate responses that will arrive.

Oh yeh! Bollocks! Here is your favoured "select loop" (not implemented by me, but rather the best CPAN has to offer to ensure fairness), processing those same 2040 urls that 64 threads dealt with in 88 seconds:

#! perl -slw
use strict;
use Time::HiRes qw[ time ];
use LWP::Parallel::Useragent;
use HTTP::Request;

my $start = time;

my $pua = LWP::Parallel::UserAgent->new();
$pua->timeout( 10 );

$pua->register(  HTTP::Request->new( 'HEAD', "http://$_" ) ) while <>;

my $entries = $pua->wait;

printf "Took %.6f seconds\n", time - $start;


__END__
c:\test>pua-head-urls urls.list
Took 1333.616000 seconds
[download]

Yup! One thousand, three hundred and thirty three point six one six seconds.

For all your claims of 30 years of experience, and fine protestations, you know nothing. You just regurgitate what you think you've read as authoritative. And usually get it completely wrong.

Can you do better than the author of LWP::Parallel::UserAgent? I'm betting you will not even try. Just like you never have.

BTW: I'm not arguing with you. I'm simply telling you that you're wrong. The only counter-argument is proof. Ie. Runnable code that supports your erroneous statements. Ante up or shut up.