No shivs allowed! (great writeup on your shiv build, btw).
Anyway, for <=150% crit dam bonus it is basically ripper vs cheap shots. In light of the new info on the order that the effects are applied, it looks like the Cheap Shots spec is better until roughly 60% health, and then for lower health the Ripper spec is better (it also depends on the exact weapon crit dam bonus, but that's roughly what is going on). However, it could easily be argued that early damage is more important than late damage, because:
a) Who the hell cares what your damage is when the opponent is at 1% health.
b) More damage early means larger ripper effect for your next attacks.
So I 'd say that overall one can choose whatever the hell he wants, but in a handwavy manner I'd say that the Cheap Shots spec will pay off very slightly better for all opponents without huge HP. Anyway, the difference should not be that important.
From a philosophy of design perspective, I 'd say that the more specialized feat (ripper) should have had the *clearly* better specialization. I am speccing in Cheap Shots with my fist builds, it is a bit disappointing that I 'll be speccing in Cheap Shots with my knife build again.