Today's swim was a record length of 2700m and took well over the hour. The routine was 3 supersets of 5 sets each that were supposed to increase in pace.
I can't say that I managed 5 increments in pace. On the whole the latter sets were quicker than earlier and naturally there was a gradual reduction across the 3 supersets. My best pace for a 167m set was 2:16min/100m although I did manage a 2:03min/100m length once.
It seems that I have a best, or favourite, pace and find working above that ineffective. That's pretty much the case for running for everyone so why should swimming be any different?