I say go 400/800 (thats what I do)
true 400/800 guys, despite what letsrunners think, are not truly middle distance runners, more of long sprinters. As such, you should not have too much "long mileage" (some is definitely beneficial, like XC in the fall) but once you are in pre-season you should keep almost all workouts to either top end speed or sustaining speed (max v or lactic)
I wont pretend to be an expert, but after XC you need some days every week of sprint mechanics and max velocity work, and maybe 1 day a week of longER intervals (maybe 4x600) but never much longer than that. What I did with my coach on other days was stuff along the lines of this
4x300 AS FAST AS POSSIBLE with long-ish (5-7 mins) rest followed by
2x150 with 3-5 mins rest all out followed by
2x60 with 2-3 mins rest
or on a different day
700 faster than 800 goal pace, 1 min rest, 100 all out, 1 min rest, 100 all out
10 mins rest
500 at 800m pace, 1 min rest, 300 all out
10 mins rest
150m all out, walk back to start, 150m all out
5 mins rest
4x60m all out
maybe only 2 of these workouts a week because they tear you down alot...
They are basically A LOT OF LACTIC ACID and A LOT OF SPEED
inb4 someone says you need a lot of mileage, I know OP is no legend but Donavan Brazier goes 20-30mpw during season... only 1 30m aerobic run per week. yes he is inexperienced, but a true 4/8 guy should keep slow stuff to a minimum.