In reply to sharpie530:
As it happens, I just did, for a change, a bit of distance swimming tonight.
Did about 10 sporadic lengths as a warm up and then suddenly decided to swim a mile, only the second time I've ever done that (I rarely swim more than 20 consecutive lengths!)
Anyway with this thread in mind, I timed (roughly off the pool's analogue clock) my first 400, in a 25m pool, freestyle but paced in consideration that I would have another 48 lengths to do afterward. It took 8.5 minutes in a shared lane with just a couple of bits where I had to slow down a bit due to slow swimmers in front.
I say I paced it, but I doubt that my "sprint" would have shaved that much off my time. My freestyle technique is woefully lacking, legs are hardly used. Did a few tumble turns but they were hardly "race style". I wonder if open water would affect this time that much.