I'm having a bit of trouble finding resources on Sieve other than it's RFC, which is a bit overkill.

I just want mails tagged by spamassassin as spam to go to a "Junk" directory and mails with a very large spam rating to be discarded completely.

I have this to move spam to "Junk" and it works fine.
Code:
require ["fileinto"];

if header :contains "X-Spam-Flag" ["YES"] {
  fileinto "Junk";
  stop;
}
I want to discard anything with a rating of 10 or higher because otherwise each mailbox collects at least 100 spams a day.

I tried adding
Code:
if header :matches "X-Spam-Level" "\*\*\*\*\*\*\*\*\*\*" {
  discard;
  stop;
}
before the working X-Spam-Flag block but this just discarded everything.