If the performance isn't good enough, you can probably increase it a fair amount by doing something like this (untested):

my %seen;
my %newip_res;

for my $ip (@newips) {
   $seen{$ip} = 0;
   $newip_res{$ip} = qr/;drop;[^"]*$ip/;
}

while(<LOG>){
  foreach my $ip (@newip) {
    ++$seen{$ip}, print OUTFILE if $seen{$ip} != 500 && /$newip_res{$i
+p}/;
  }
}
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If there are more than a very few lines that don't have ";drop;" in them, also put a  next unless /;drop;/; just before the foreach.