All my PR's were even splits unless it was a hilly course. On flat courses my miles didn't differ any more than 5-6 seconds. I always ran every race mile to mile. A 5K was three one mile races, a marathon twenty six one mile races. I never thought beyond the mile I was running, but then again I was never very fast. 17 minutes for 5K, 36 minutes for 10K , 1:19;50 for a half marathon. That was about it. In the '70s & '80s I was lucky to finish in the top 10-15% of the field and never placed in my age division.