Hiyo!
I realize that this may run afoul of some other objectives, particularly those where people want to know all the tests that matched, and perform supplemental checks based on that info, but I have to wonder, could we improve the efficiency of SpamAssassin by having it make note of the 'HITS-REQUIRED' score and have it STOP TESTING after it surpasses that score?
This is a pretty long thread, but one thing that surprises me is that nobody (not even Justin) has pointed out that SA has already had this feature, and it was removed because it was so problematic, and actually made things _worse_ for SA instead of better.
The 2.3x series had a -S switch to do exactly what Charles suggests.
Here's the bug that killed it:
http://bugzilla.spamassassin.org/show_bug.cgi?id=304
Basicaly, the historic gist is that in order to make it work correctly, you have to run the rules in batches, negative first, positive last. And this re-ordering forces every email to have to be run through twice, which slows SA down quite a bit.
As Justin did point out, the current situation of autolearning, etc complicates matters quite a bit more, but the fundamental problems haven't changed since 2.30.
