You said that 10x400m is done at mile pace with a lap jog or 3 minutes recovery. I did 12x400m the other day on slow 200j with about 75-90 seconds recovery in 78,77, 73,72,71,then 72s and 73s. It was hot, but I felt very fresh the next day. For 10x200 recently with 200 rest (before and after I did 10x100 in around 16-17), I ran 33s and 32s, to indicate that my top speed isn't much faster. Forget about the first two 400s, where I was still warming up.
Should I really take the 71-73 to be slower than my mile pace right now? My pr's are 4:39 mile/9:20 3k/16:04 5000m. I'd think that around 4:50 would have been closer to my mile if I had been racing the other day, so that the 400s would have been at mile pace.