Your splits look very good to me - I wish I could do times like that for 25m, never mind 50 yards.
I remember seeing somewhere a set based on the goal final 50m of a race. The idea was to swim large numbers of repeats at the pace you hoped to be finishing your race in. As the set progressed you came closer and closer to the physical state you would be in on race day on the last few meters (or yards). At the same time you were building neural and muscle memory of how that pace felt. Because your second 50 is always slower than your first, initially the pace would be relatively easy and over a period of time the whole set should become easier. That's the reasoning as far as I understand it.
I would be interested to hear Terry's views on this approach.