*COUGH* back from my absence, I was re-reading here...
a) No need to wait for paragon level for ferocity to give you temporary hp. After the errata, battlerage vigor gives temporary hp every time you hit with a melee or close attack.
b) Since I wouldn't say the dying condition is an "effect", I stay pretty sure that temporary hp keep you from going unconscious, or dying. If they don't, they're just the same as limited damage reduction.
c)being able to push and knock prone on an OA is not that easy. You can do it at paragon, or maybe even earlier, if you're a fighter, but there's more classes that don't have access to that kind of at-will. So it's an option. Also, Tide of Iron requires a shield.
That said, I agree with Covaithe here. It seems an easy choice, but maybe not the wisest.