To simplify, here is my proposal:
(1) Stats
Include what KLOL and I have listed for real life electricity properties and data.
Maybe also add that electricity can go up to 90% speed of light in conductive metals.
(This is important for determining what proxies apply what speed)
(2) What electricity projectile is I wonder if the form of lightning should be considered.
If the "electricity projectile" exhibits properties of an electric dart, a taser projectile speed (50 m/s) should be applied.
If the electricity projectile exhibits mostly pure electricity properties but the whole casting does not exhibit lightning, the supersonic to hypersonic speed could be applied.
Also, if the electricity projectile is shown to travel as "slow" as a bullet (e.g. those cheesy cartoons), the supersonic to hypersonic speed could be applied as well.
If the said electric projectile is cosnidered lightning and exhibits properties of a leader strike, the 440,000 m/s speed should be applied.
To discuss: what is the minimum criteria for a lightning leader strike?
If the said electric projectile is cosnidered lightning and exhibits properties of a return stroke, the 100,000,000 m/s speed should be applied.
To discuss: what is the minimum criteria for a lightning return stroke?
If the said electric projectile can travel at conductive metals, said projectile while through "conductive metals" can be marked as 90% speed of light.
(3) "Possibly" proxies
To discuss: What KLOL says: Can characters be proxied to be lightning level by "verbal descriptions of degree of control over lightning and electricity".
(4) Attack potency
Generally agreed: real natural cloud-to-cloud lightning counts 1.6 gigajoules which is 0.38025 tons of TNT, and real natural cloud-to-ground lightning count half as much.
To discuss:
1. How tanking electricity accounts for durability? (Like, there are lucky real life individuals tanking real life lightning. They are likely not 9-A+ or even 8-C.)
2. Does one character which can cast a natural lightning strike from itself (e.g. a magician using a wand) have 9-A+ or 8-C AP?
(Now I think about it, that should be normally 9-A+ because that should be what a natural lightning would hit a grounded target.
Unless you want to say 9-A+ against grounded target, 8-C against a target airborne or near heavily charged environment)