Hello there, @tpower. I can’t answer your first question as I have never done SSB HV. However I did SSB MV and still changed since it was a little bit too much (intensity) for me. For reference, I have been doing 650+ hours for a couple of years now, changed from running mostly to riding almost exclusively. What I can say that even if I have CTL above 110 I wouldn’t want to do SSB HV, the spring is too far ahead and I would burn myself out.
This winter I will repeat what worked last winter and change it just slightly. I’ll do even less intense workouts (more tempo) but I’ll try to do more intense easy sessions, upper Z2 zone. Sorry for shameless self promotion but I don’t think that winter is the time for much of an intensity. Leave that for the KOM hunting or racing during the season.