You could do something like this.

opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
my @files = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
closedir(DIR);
@files = sort {$a <=> $b} @files; # Ascending sort

my $count = 1;
foreach (@files) {
   rename($_, "testfile$count") or warn "rename: $_ : $!";
   $count = $count + 1;
}
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You don't have to use a separate file of sorted file names. You can use the code above or a variation there of to get the job done. In reading your post I saw you wanted the files not to correspond to their number (ie: 2 != testfile2, 2 == testfile1). This can be done by keeping an incremental count. If you want to keep the separate file of sorted filenames just ignore the first part.