Skipping SpamAssassin w/ high number of RBL hits

[Gregg Berkholtz]

I'm using a ruleset to skip SpamAssassin when the From address matches
whitelisted domains that use SPF - this alone greatly reduces my
server's load.

Though I need to further cut the load, and considering a good chunk of
inbound spam is already being caught through MailScanner's RBL checks,
is there any way to skip SpamAssassin when a message has, say...3 or
more positive "Spam List" and/or "Spam Domain List" hits in MailScanner?
I was thinking a ruleset directive like "From:" or "To:", but instead
they'd be something like "spam:" or "rbl:". I cant find any indication
these options exist.

Thanks for any help!
Gregg Berkholtz