I like the 10×400 (Roger Bannister’s Workout), this workout is often misunderstood. Bannister did this workout because it is was the only way he could maximize his schedule as a medical resident and elite amatuer track athlete. He used it as a guide to pacing and building strength. The workout must have at least 2 days to recover from. Meaning the 2 following days must be accompanied by an easy run then a day of easy strides just off race pace goal.
10×400 for 4:20 1600 = 65s per 400 pace. That should your goal. Anything faster is probably useless and will hurt you race day.