YD, it's interesting that someone like you with good endurance can run longer races at such high HR %ages. Last time I checked my 10k was about the same as your 10-miler, and 5k was about 95% average.
I've seen anecdotal evidence (don't ask me where from - I can't remember) that runners with stronger endurance can hold higher intensities for longer but I don't know if there's any scientific evidence or basis for it.
Curly - bad news for Magpie! Hope it recovers soon for him.
Simon, nice session. 400 stuff is a bitch to get right. Best way I found to approach it is to try and get a reasonably high cadence (higher than say 800/1500 but not maximal) and keep stride length a bit longer than 800. Difficult to describe, it's best to play around with it (and, dare I say, experiment with in races).
You will need to improve 400 speed to stave off hitting the glass 1500m ceiling, but it looks like you're going about it. I've been doing 2*5*100 w/walkback which has worked quite well, as well as 6*200 at 'comehome' pace (the pace you'd expect to run the second half of a 400 in).
2*4*400 today, 60s between reps & 4 mins between sets. Better paced than Wednesday
- 71.7, 71.9, 71.4, 71.2, 70.7, 70.0, 70.1, 69.3. Felt tired but more good running in the bag.
Didn't make the Proms 3k today as I had to work, but I've been hearing high winds so hopefully no times to threaten my series second place 
Edited: 01/02/2013 at 16:26