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sleeping bag is much more efficient (space and weight-wise) at keeping you warm whilst at rest than a jacket.
understand if you like yours, but I think insulated jackets are a waste of time if you're going fast. you're not going to be sitting around waiting at any point, so a sleeping bag keeps you warm during your only rest periods. and as soon as you start cycling, insulated jackets overheat.
platypus-
I can't wear a sleeping bag whilst cycling though :p
I could be wrong on this, but I think there'll be plenty of times where I'll be pedalling slowly, or on descents, not at all, at night time. Those are the times when the jacket will be handy.
I'm trying to avoid making the same mistake I've made the in the past where I go out on slow rides - assuming that what works for a quick tempo effort will be good for long/slow/steady rides. My body doesn't produce anywhere near the same kind of heat which means I need to wrap up a little warmer. Adding fatigue and nighttime/long descents/high elevation into this means an insulated jacket (especially a breathable one, designed for riding in) makes sense.
edit: I still might take the sleeping bag too. I'm going to see how I get on with the bag, the bivvy and the mat in a few weeks with 3 nights bikepacking in Scotland.
gillies
Still considering leaving a sleeping bag and just taking the bivvy and mat - in which case the jacket will be used for sleeping too. I think either way, the insulated jacket will be coming as its pretty packable and its insurance in case of something going wrong - a mechanical stuck in the mountains, for example.