Tai
In college we ran them at about our 10k pace minus 7-10 secs per 400 so 5:35 per mile would be run at about 5:00 pace or 75 secs. This was strictly running and is pretty much the text book way - for triathlon I would still run them fast if you are training for Olym distance or shorter and the rest should be about a 200m jog. I don’t believe in standing around unless you are doing mile repeats or longer. IF you are racing longer distances then 800s, 1ks and miles are better in my opinion. I know lots of tri guys who do absurd #s of 400s - like 25-30 - maybe it works for them (?).
Mike