I'm going to have to disagree with you there Azrael. When playing the 3 note per string scale..DO NOT sweep. alternate pick regardless.

Personally, I grew up (on the guitar) by doing that sweep and I sort of regret it. I won't say that you can go faster with strickly alternate picking, but it sounds much better. I have found that with that sweep technique, you sacrifice a clean rythem. I almost always "gain" a beat after one of the string sweep lines which throws timing off, and It took me years to find out exactly why. After I adjusted to alternate picking, the problem vanished. I wouldn't make it a habit of doing that sweep technique.