With cup and core bullets, of equal construction, the higher SD bullet may not kill any better, but they will absolutely penetrate deeper (270/150 vs 308/150).
If all else is equal, perhaps. SD is a metric oft relied on to riddle expected results, but there are so many other factors at play that it is a guess on the best of days. It is nothing more than a ratio of weight/diameter that will begin to change as soon as the target is met. What is the SD when 30% of weight is lost? What is it when the bullet begins to tumble. The world of terminal ballistics is one of the last remaining scientific black holes in shooting sports and I suggest one not spend a lot of time theorizing about what happens and the results thereof. Just put the bullet where it needs to go.
