DR - I hear you mate, thought NOS Life was is/a troll. The thing that blows my mind though is that Wanjiru's 1/2M WR pace is more or less what NOS Life quoted for their 2 x 6M workout.
2TM - Agreed, there's plenty of useful discussion as the week rolls forward and I'm finding it a very supportive and friendly thread. FWIW, I'd find it odd if you didn't find 5:20 pace to be tough. 5M/8k race pace is a hard pace, especially in the middle of heavy training as BB points out. Invariably, if I'm doing a 10k effort reps session, the first couple are ok, but the last one or two and I'm breathing hard and beginning to hurt. Agree with pablo, doing this type of session alone always makes it tougher too. As niarun mentioned, find that a session or two of strides each week definitely helps with form, which in turn makes 8k/10k pace/effort reps feel easier. Tend to avoid doing VO2 reps unless I'm in the final few weeks of sharpening for a key event, so I basically never go on the track.
JewOn - Incredible marathon history, you've been running excellent times for quite some while. I'm 40 too and don't plan on slowing down anytime soon, so don't think you should either! How did you feel at the end of the 5:34 pace half? Was that a comfortably hard run or all out? Again, I'd suggest trying to work in a couple of "Pfitzinger-style" 20M incorporating ~13M @ marathon pace and see how they feel. If you can get through those without flogging yourself then I reckon you'll be golden following a good taper.