while ($sth->fetch()) {
	# do comparison
}

##</code><code>##

my %sites_list;
@sites_list{split(" ", $sites)} = ();		# hash slice for quicker lookup

while ($sth4->fetch()) {
	if (exists $sites_list{$newSiteNumber}) {
		print "modify!";
	} else {
		print "delete!";
	}
}