optimal split differential between 50s in 100

what is the optimal differential between the first and second 50 on a 100 yard short course freestyle? The first 50 benefits from the dive and the relative freshness of the swimmer; the second 50 requires two turns and contending with lactate and fatigue. Is it better to go all out and try to hold on, or save a little for the end? Say you can swim an all-out 50 by itself at 25 seconds. How would you ideally swim the 100? Example: 25.5 then 28.5 for 3 second differential and a 54.0 or 26.0 and 28 for a 2 second differential and a 54. Which method do you think is best?