PS4 is not 2x Xbox One on Tomb Raider

E. Xbox One is artificially locked at 30FPS, if it was unlocked it would surely average higher than 30 FPS, probably closer to 40 FPS.
Given that information and the fact Destiny has the same performance profile on Xbox One it is not unreasonable to think that without the FPS lock Destiny would average around 40 FPS on Xbox One as a minimum. Going one step further to then say the PS4 should be able to achieve around 55 FPS as a minimum is another reasonable thought to have.
So in answer to the original question where a poster asked how much extra work (or not) would it have required to hit 60 FPS the answer is not a lot, a stable 60 FPS though would be much harder.