Report from the last few days:
The 5x2K session was very hard running at a 4:05 pace. Perhaps I was not fresh enough to do such a session. It started out fine, but pace dropped on the last 2K ending in the 4:10-15 range and MaxHR dropping as well - not good, but I finished the session.
It was nice really nice to have a rest day and the long run felt solid. I did 1h 20m easy.
Today I felt fine and did a 40min 'not so hard' playing a little with ½ marathon pace doing 4K at 4:25 and the rest easy.
So the status is the 4:25 - 4:30 pace feels really comfortable and my feeling is that this should be ok for a ½ marathon by the end of december. The question is if it is ok to use the easy runs to play a little bit with pace or if they should be so easy that it is only recovery / preparation sessions?
Is it all ok to run use the program like this, still trying to get faster on 10Ks while upping the easy runs with distance and a bit of pace play for ½ marathon?
In any case I feel fine and strong (if not fast) and are really enjoying a new level of running fitness :-)