3.5-5% Strength for 3.5s on Hit. Stacks 5 times.
Up to 5-20% Strength based on the charge time of your heavy attacks. Stacks 3 times.
Your Grenades stick to Ogryns and Monstrosities. 6-15% Damage vs Ogryns and Monstrosities
5-8% Strength for every shot fired during continuous fire. Stacks 5 times.
This is what I have been running in havoc. Honestly, for ogyrn, it doesn't seem to matter anymore. His entire tree is good. It is hard to go wrong. I would say that flex is Payback Time and Strongman. I have tried Dominate and Bash and Blast. I have tried Implacable and No Stopping Me!. No Stopping Me! feels really good and is fun, but I am not sure it is worth the straight damage from Payback Time. No Pushover and Hard Knocks are also really good, but that is 3 points that I don't have. Another flex could be Slam, but I like slam and Pumped Up together.
You could take any pick axe with this build, but the Branx Mk Ia Delver's Pickaxe in particular excels at boss damage. It also very easily killed crushers and bulwarks in one hit with Thrust and no other buffs up. If you don't want Thrust, then Slaughterer or Thunderous(if your team doesn't have other ways to apply brittleness) is good. The Branx is really good at eliminating single targets in one hit, which is very useful in havoc with the rage (red) and garden (purple) buffs. Things do not get a chance to rage. I have also tried this build with the Krourk Mk IV Cleaver and it works pretty good. Any weapon that utilizes heavies in their chains works here. In normal auric missions, I prefer the Borovian Mk III Delver's Pickaxe, as it feels more fluid and natural to use. If not using a weapon that uses heavies in chains, then get rid of Beat Them Back and Crunch! and use something else, but you would probably want a different build, as this one is tailored to the Branx Mk Ia Delver's Pickaxe.