"Big & Slow" and "Small & Fast" as stand alone terms have no meaning whatsoever if we are not taking in consideration bullet construction, shape, SD and energy.
Mostly B&S and S&F are matter of opinion and preference too often with no real scientific/technical backing.
Hydrostatic shock has never been scientifically proven without doubt to contribute to quick death, small local hydrostatic shocks (and only in very high velocity rounds) have been observed, how they contributed to lethality is a very open question.
As we said in another thread before the only undisputable facts is that bullets kill destroying tissue along their path and penetrating enough to reach vital organs. The contributing factors are, bullet diameter, velocity/energy, bullet sectional density, shape and construction, all the rest is speculation.
Speed kills more indeed, all else being equal...nobody is going to dispute that a modern 45-70 loading at 2000 fps is more lethal than its original BP counterpart at 1300 fps, the first is considered a decent Arican load the second is not.
The real equation and question to think about is, when you fire a "big and slow" bullet compared to the "small and fast" in a specific scenario is what bullet is going to destroy more tissue and penetrate the most, the one that does that is the most lethal indeed.
So in that specific scenario if the small and fast bullet is going to espand to a larger diameter (sectional density constantly changes when a bullet expands) than the bigger pill and penetrates more, technically the small and fast is more lethal, period.
That said, finally, every shot at an animal is different and odd things happen sometimes.