A power fist could be a good way of proccing Cull the Weak more often, but it only knocks the foe backwards a third of the time. I think I was unlucky that there wasn't an opportunity to use it in my last game - there is usually a chance that someone will want to avoid getting hit by a chainfist and move away, but I was on the back foot early on and he was feeding me engines to slow me up.
It's cheap so I'm happy taking it along just in case I get a double hit, but I don't think I'd build my force towards it, especially as you have to use a princeps trait to take more than one too.
A quake cannon could also be a good option - I will be trying a more shooty force next time and will give it a go.
I've not tried scent of blood yet, out of turn activation is tasty but I have a lot of Warhounds and they can't afford 2 heat!