I have no idea which numbers are which in today's latest patch, but shield slam has ALWAYS been behind other skills for rage efficiency. Shield slam is most useful for a secondary snap-aggro skill for when taunt is on cooldown or when you absolutely need that mob off someone without having to switch stances for mocking blow or burn a 10 minute shout.
Because the value posted above shows SS to be less Rage-efficient than Imp. Sunder (in fact, less Rage-efficient than unimproved Sunder), which would makes its value rather limited.
This is the build I used when I was prot specced. LOL at imp. revenge, but it was fun for sartura. You have quite a lot of flexibility with prot specs because half the tree is garbage/filler.