My first question is how long have you been doing intensive tempo workouts? Special Endurance is broken up into two parts. Special Endurance I is any distance between 150-300m with full recovery in between each rep and a maximum total volume of 1000-1200m per session. Special Endurance II is any distance between 300-600m with full recovery in between each rep and a maximum total volume of 1200m per session.
As far as you and Trck400mRnnr's race strategy, this is how you run a 400:
1. Run the 1st 40-50m hard. Get out aggressively and push to the 1st 50m. Since you don't start oxygen debt in a sprint until after the 1st 6 sec, it makes the most sense to go out hard for the 1st 50m, which is about 6 sec, depending on how fast you are. Going out hard for the whole 100m would cause you to go into oxygen debt a lot sooner.
2. Once you get to 50m, you should relax. Don't slow down, just don't try to go any faster. This is the part of the race where Michael Johnson looks like he's jogging. He's actually going pretty fast, he's just relaxed. So once you get to 50m you should relax. You'll do this for the next 150m.
3. Now you???re about to go into the curve (3rd 100m). Right here is where you should become aggressive again. Because what you want to do here is maintain the pace that you've been running. To do this you have to be more aggressive with your arm action. Pumping your arms more will take some stress off of your legs and help you to put an overall effort into keeping your pace. This is the part of the race where Michael Johnson used to look like he started to run faster. But he actually wasn't. He just didn't slow down.
4. Now you???re getting on the straight. Right now you???re "probably" a little tired. Right here what you should do is relax and concentrate on your form. Lift your knees, pump your arms back and forth. Try to exaggerate your form. When you do this it may feel like you???re bringing your knees up to your hips but most likely they're not. The closer your form is to being good the faster you'll go in the last 100m.
The whole idea of running the 400m is to spread your available energy through out the whole race. You want to avoid hitting the wall for as long as possible. This is Michael Johnson's real race strategy. And if you do a bit a research on how the human body works you'll see why this is the most effective strategy.