I've been pumping up my Stern L2/Coggan L3 volume, as prep for 2x20 L3/L4 (as mentioned in that earlier thread). So far so good. I'm ignoring HR, and not even looking at it.
60 min TT power = ~235w (slightly conservative, I think).
Tempo L2/L3 power = ~175-210w
Yesterday I did 1x75 mins, 197w, 199w normalized, felt fine. I could fairly easily do that for 2 hours, I'm sure. When I got home and check HR, it turned out to be a steady 170-179bpm, avg = 177, with no material upward drift. But that's 90% of MHR! For Tempo?!
I don't know if that's OK, but just for reference, the Tempo HR zone from CTS was 156-159bpm. 177 avg is even above their climbing repeat zone.
It'll be interesting to see whether I flame out are greatly improve from this huge increase in intensity. I can tell you this, though, it makes riding more fun... and faster. :-)