I just did these two track workouts over the last two weeks and I know they're good because the hurt....bad. Anyways the both help get you into a good rhythm and help , I think, to flip the switch especially when your getting tired and that's what you need to do in a race. I of course go too fast and try not to die so I hope that these workouts help me run a little smarter and make me a little tougher. Maybe they'll do the same for you.
Workout 1#: 3 mile drop down. First mile at about half marathon pace, second mile at 10k pace and last mile just drop the bomb and try to run 5k or better pace. I did 5:40, 5:30, 5:15 for a total time of 16:25. I was hopping to run under 5:10 for the last one but it was not to be.
Workout 2# : 2 X 3K. Run the first 2k of the 3k at 10k pace then try to drop the hammer on the last 1K. I took like 5 minutes but the rest should be 3-5, 5 being the max, and I needed it. I went 3:20, 3:20, 3:16 (9:56) for the first set and 3:20, 3:20, 3:17 (9:57) for the second. Not great but adjust to your own ability level. Peace