If you just want to verify that the file is there, try a HEAD request instead of a GET request. If that gives you a false negative (it might, depending on the server), then set the max_size attribute of your LWP::UserAgent object to something like 512 bytes, so LWP will abort very quickly:

my $ua = LWP::UserAgent->new (max_size => 512); # note extra param

my $tmpfile;
foreach my $rev ("-", ('A'..'Z')) {
  $tmpfile = "$file$rev.$ext";
  my $response = $ua->get("$path/$tmpfile"); # simpler interface
  ## you need to save $tmpfile here!
  last if $response->is_success; # better than yours
}
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-- Randal L. Schwartz, Perl hacker
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