I ran almost exactly these times in high school (a long time ago). I'd echo previous posters' sentiments about not focusing on hitting specific paces and rather just going off feel (which you should have developed a pretty good sense of by now). Your goal should be to get in a good, hard workout, not to hit xyz pace.
I also agree that you don't really need to be doing hard track workouts now. Consistent mileage, weekly tempo runs, and regular strides are all you need during the winter (and no need to do the strides every day at a dead sprint - a couple times a week at 800 pace is fine).
That 4x6, 4x4 workout looks great, but you can throw that kind of stuff back in in March. My key workouts were fairly similar. Some of the ones I did, off the top of my head:
2x1200, 3x800, 4x400
6x1000
1600, 2x800, 4x400
12x400
8x400
Speed work mostly came from strides and racing a few 800s and 4x4s