I think the fundamental problem is that "electricity" as you describe it, doesn't actually exist. The word "electricity" has many separate and contradictory definitions, so it cannot serve as a useful term in physics.
Analogy: if you were asking about the "speed of optics," nobody could answer, since the word "optics" could mean several completely separate things. The speed of falling lenses? :) To ask a meaningful question, ask about the speed of lenses, or perhaps the speed of light, and avoid the word "optics."
In a similar way, the word "electricity" lacks any narrow scientific definition. No single "electricity" exists. The word is commonly used to refer to propagating electromagnetic energy along wires (which moves at nearly the speed of light.) But "speed of electricity" also refers to the flow of charges during electric current (which drift along at centimeters per minute and less.) The word can also mean any electrical phenomena: wires are electricity, sparks are electricity, batteries are electricity (but transistors aren't electricity, instead they're electronics. See, confusing!)
In other words, sparks aren't made out of "electricity," any more than lenses are made out of "optics," or bicycle gears are made out of "physics." To ask a sensible question, avoid the word "electricity," since it has multiple contradictory meanings.
Speed of electrical energy: roughly the speed of light, but lower than c because of refractive index of cables' dielectric.
Speed of electric current: very slow "drift velocity" of charge carriers, but it's proportional to the current, conductor size (sectional area,) and to the carrier density (e.g. metal versus salt water versus electron beams.) High current gives fast carrier-drift, and at zero current the charge-carriers come to a halt.
What is the speed of leaping sparks? Sparks are an example of electrical plasma, also called "plasma streamers." The speed of a visibly-leaping spark is the speed of tip-growth of a plasma streamer. When a plasma-streamer extends itself, the plasma isn't moving along. Instead the nitrogen and oxygen in the air ahead of the spark is being converted into plasma, which adds to the tip of the growing leader. Lightning is a progressive converting of air into plasma. In other words, lightning is actually a "lichtenberg figure" made of nitrogen-oxygen, rather than being made of damp wood. These wood-fractals are made by converting insulating wood into conductive carbon paths, while lightning is the converting the insulating air into conductive plasma paths.
Such growth can have many different speeds, from zero speed of non-growing coronas displayed by Jacob's Ladders and by tiny Tesla coils, to the easily visible growth of Anvil Crawler lightning, to the extremely rapid propagation of "stepped leaders" in a larger lightning discharge.
See examples both of stepped and continuous lightning leaders, 9,000FPS video:
Or, see "anvil crawler" lightning patterns spreading relatively slowly across a horizontal storm-base: