Marshall – the plan you proposed is just another short-to-long approach where the "short" section is just prolonged. Sounds good, though.
I agree with what both you and Rice said with speed reserve, though.
But, here's my biggest issue. I don't think (in fact I know) that I won't be capable of a 49 sec. 400m until my 200m speed is below 23.0. There's just no way. That's why I'm debating on spending next season on endurance with speed-maintenance to bridge the gap b/t my 200m pb and 400m pb (about 6 seconds now) or to work on speed with endurance-maintenance sessions to bring my time down more off speed and then train for endurance later. That's the real point here, for me.
But, that raises another question — is it easier to train for speed or endurance and should you train the easier or harder component first?