It's extremely important to note that you will want to have 3 Fell Cleaves and 1 Fracture every Berserk period whenever possible. This is normally for boss fights. Still very dependent on the fights themselves. Priority order: Fell Cleaves > Fracture if you can't afford that last GCD in Berserk for Fracture, use 3rd Fell Cleave instead.

Rotating Fracture in each mob is questionable. If you are talking about mobs tanking, Overpower is usually better as there is usually at least 3 mobs to hit, rarely 2 mobs. Off the math, 120pot x3 is better since it's instant and more damage, also enables you to hold aggro better if you are struggling at it.

Flash is something you don't really use except for a few situations: 1. You are on the 5sec pacification. 2. You want a full 360 degree aggro rather than a cone AOE. Antitower mobs after 2nd boss for example spawn themselves in extreme left and right, Overpower won't reach them unless if you position yourself properly, which I normally flash twice to grab all 4 mobs quickly and do massive pulls. 3. You have no more TP and you need to aggro.