Teach me when to use Onslaught.

[Felorr]

Here's a basic that should tell you everything you need.

You have two zerk windows at 70 right? The one that allows you to do six cleaves and the one that gives you just the three cleaves. Now, between these windows of zerk you'll find that you'll get close to your max gauge quite a bit before your next zerk is ready, that's why you use onslaught and upheavel (do it early after you finish your zerk cleaves, not later on only when you get close to the max gauge)

I wanted to build further on this. Keep an eye on your berserk cooldown. Here's how much gauge you will generate in various intervals like 15 seconds and 20 seconds.

About 6 GCDs within 15 seconds nets you:
50 gauge minimum (if SE/BB is used within this time frame)
60 gauge maximum

About 8 GCDs within 20 seconds nets you:
60 gauge (if you start with HS into SE. OR if you start with HS into an SP into SE combo.) 22% of all possible GCD combos within 20 seconds.
70 gauge (if you start with SE, or the HS after SE, or either of the two SP's during this window.) 44% possibility
80 gauge (if you start with Maim during a 20 second duration.) 33% possibility

So what does all of this mean? You glance at your Berserk CD, Upheaval CD, your current Beast Gauge, and your Storm's Eye timer. You determine roughly (give or take 10 gauge) how much gauge you'll get in that timeframe, keeping in mind to use SE near the end of that time. Safely assume you're dumping 20 gauge with Upheaval, and now need to determine how many more intervals of 20 you need to drop to avoid overflow.

This usually means, onslaught twice, upheaval once. This means you must use onslaught in advance, 50 to 60 gauge (like +20 seconds left on Berserk CD) to ensure the it is ready again. If you wait until you're at 70 gauge or above before using onslaught, you'll overcap before the CD is back up.