What should my goal mile time be as a 200/400 runner

I think 5:30 is a good mile goal for your JROTC testing

my best events were 300H/400, also did 100/200, and i found XC helpful for teaching pacing, improved endurance. XC takes away top gears for 100/200 -- which are more of a drag race -- but for the 400/800 can help you close better.

some of the 400 is getting your pacing/200 splits right. sometimes a second slower at the midpoint lets you run the second half closer to the same split which proves faster overall.

i am also going to make my usual sales pitch. an ok 400m runner with endurance can sometimes be a good 300H runner if they can handle hurdles. 300H there are usually fewer runners entered. many of the 300H folks are mediocre speed 110 high hurdle people doubling at an event too long for their fitness or speed. if you have some foot speed and can get over the hurdles efficiently, you can kick their butt.