DOS potential?

[spamassassin]

  I've recently added chickenpox.cf, backhair.cf, and bayes since more 
and more spam has been getting through. They work great! Spam has been 
cut back down to what it used to be awhile ago. Thanks guys and gals!
  Something I did notice though was that a few kb email received a huge 
38pts. Now, I didn't do any time tests on that email to check how long 
it actually took to process, but I'm assuming longer than one that only 
scored a little over 5pts. I am wondering if it would be possible for a 
spammer / dos virus to flood a smtp server with a email that was crafted 
in such a way that it would score as high as possible and or find tests 
that take longer than others while maintaining a very small file size. 
I'm imagining that, enough email would make a server crawl and start 
causing smtp timeout problems. Should there be an option to tell 
spamassassin to stop checking and tag the email after it has received a 
5pts limit? Kind of a "Why keep looking at it after I know its spam?".