I think it all depends on your training. I've definitely sacrificed speed since getting into ultras, but then most of my runs are long and slow, so what do you expect. Those who continue a more marathon based training regime, with tempos and speed work, probably hold on to their speed a bit better.
I've heard the advice of flipping the usual winter base period, in season speed work, for ultras, as all race season is pretty slow by definition, so the off season is the time for speed and strength. If that makes sense.
I'm going to be getting a 920XT soonish, so depending on how imminently you need it, I could send you my old 310 so that you could get an idea of what features you might or might not need. Let me know.
I would say forget the specific plans, and just do more of what you enjoy, you're more likely to stick to it that way. I think ultras are more about lifestyle than schedules. But that might just be me. Enjoy trotting along in the countryside and don't think of it as a chore, and you'll be right.
Yeah, I do the charger thing in my hundos, but anything that takes away that faffing around is a great help, especially when I'm at the stage when opening a gate is like the krypton factor, and stepping up a curb is like an obstacle race.