I'm bumping this again because it seemed quite a few were gunning for this goal. How's everyone done?
With regard to me, I am not really targeting the 400m any longer - I enjoy long, quick runs too much, and always enjoyed the HM (username checks out). I'm running 65 mpw all moderate/easy atm. The next week, I'll do that again, but include three or four sprints with full recovery after each run other than my long run. However, the purpose of those sprints is to keep in touch with top speed, making interval paces much easier, and improving running efficiency, rather than as 400m training. Within a month or so, I'll be at my goal of 65mpw with one hard tempo, one short interval session, one long run, one short recovery run, and three moderate runs of around 9 miles. The idea is to try to hit some good 10k/HM times in a few months.
I'll still likely time-trial the 400m a few times, and it would be nice to see if I could sneak under 60 on this training, but it's no longer the primary goal.
I didn't want this thread to die, though, as it seems many have the sub-60 goal. Good luck to you all!