mail load and spam/virus checking curiosity

I have a curiosity. O:-) On my home system, where I connect through a modem and download my email with fetchmail, and pass it to postfix + procmail + SpamAssassin + amavis, I see that the system load goes up to almost 100%, and there is a delay in the mail queue of 30..60 emails (from this list most of them, thus, small). And this is a P-IV @ 1800 with 750 Mb ram, not a slow system. What would the impact of that be on a bigger server, say, a business one? Is it worse, or perhaps better, because it is not so concentrated (no fetchmail)? -- Cheers, Carlos Robinson