If you're at the point of shooting for this, there's not alot that can really help you.
That being said, I achieved this by using Hyperspeed on some of the harder songs (Raining Blood, Before I Forget) because I personally find it easier. Some people find it makes it harder -- It's personal preference.
I found I was ready and able to knock this over in the same day that I beat Through The Fire and Flames on expert, and by a small margin. So use that as a comparison. If you haven't beaten TTFAF, chances are you aren't ready for this.
5-star Expert cutoffs for Guitar Hero III can be found here, courtesy of ScoreHero:http://www.scorehero.com/songstats.php?stat=2&group=4&am...