> Don't mix drinks, i.e, wine with whisky

Is this not just superstition?

I've found that people's thinking for this comes from either your first point about sugar, or from failing to update your expectations when you go from, say, drinking pints that will take a while to metabolize, and then taking shots that are going to hit you hard and fast with the expectation that they work at the same speed.

I've never heard a reason that, say, a shot and a beer would make you more hung over than a shot and another shot distributed in a beer's worth of water (so it lands at the same pace).

I've heard that carbonation in some drinks acts as a more efficient alcohol delivery system, so mixing heavily carbonated drinks (beer) with higher proof ones (liquor) will maximize absorption and potentially lead to a stronger intoxication / hangover.

That makes sense! There are some funny "beer will hydrate you faster than water after cardio" studies that work for this reason.