Ed, again, thanks for the info you provide ;-).
Regarding 'not all runners are the same', I don't really fit in your 'rule of thimb' regarding easy runs.
For example, if I go on an easy run at a pace 1min slower than my 10pace, say 5.10-5.20/km my HR will definetly go up to 160. I will do a test next week to see what's my avg hr at a 5.10/km pace.
At the moment, easy run paces are around 5.40-5.50/km with avg hr being around 149bpm(upper Z3 aerobic zone).
I entered a race this Saturday on 21'th October, 22km trail, 700m elevation. So I figured I'd do the last week of the cycle, but instead the 10x400m today, I did 3x5min @ race pace with 2.30min easy in between. On Thuesday I'll do the 6x1min session.